Transition metal composite hydroxide capable of serving as precursor of positive electrode active material for nonaqueous electrolyte secondary batteries

ABSTRACT

A transition metal composite hydroxide can be used as a precursor to allow a lithium transition metal composite oxide having a small and highly uniform particle diameter to be obtained. A method also is provided for producing a transition metal composite hydroxide represented by a general formula (1) MxWsAt(OH)2+α, coated with a compound containing the additive element, and serving as a precursor of a positive electrode active material for nonaqueous electrolyte secondary batteries. The method includes producing a composite hydroxide particle, forming nuclei, growing a formed nucleus; and forming a coating material containing a metal oxide or hydroxide on the surfaces of composite hydroxide particles obtained through the upstream step.

The present application is a divisional application of U.S. patentapplication Ser. No. 14/123,410, filed Dec. 2, 2013, the contents ofwhich are hereby incorporated by reference in their entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a transition metal composite hydroxidecapable of serving as a precursor of a positive electrode activematerial for nonaqueous electrolyte secondary batteries, a method forproducing the same, the positive electrode active material fornonaqueous electrolyte secondary batteries, a method for producing thepositive electrode active material for nonaqueous electrolyte secondarybatteries, and a nonaqueous electrolyte secondary battery using saidpositive electrode active material.

2. Description of the Related Art

In recent years, with the spread of portable electronic equipment, suchas cell phones and notebook-sized personal computers, development of asmall and lightweight nonaqueous electrolyte secondary battery having ahigh energy density has been strongly desired. Also, development of ahigh-output secondary battery as a battery of a power source for drivingmotors, particularly a power source for transport equipment, has beenstrongly desired.

As such a secondary battery, there is a lithium-ion secondary battery.The lithium-ion secondary battery comprises a negative electrode, apositive electrode, an electrolyte solution, and the like, and, asactive materials of the negative electrode and the positive electrode,materials capable of desorption and insertion of lithium are used. Atpresent, research and development of such lithium-ion secondary batteryare being actively conducted, and particularly, since a 4V class highvoltage can be achieved by a lithium-ion secondary battery using alithium metal composite oxide having a layered or spinel structure as apositive electrode material, the commercialization thereof as a batteryhaving a high energy density is progressing.

As a material which has been mainly proposed until now, it may includelithium-cobalt composite oxide (LiCoO₂), which is relatively easilysynthesized; lithium-nickel composite oxide (LiNiO₂), in which nickel,more inexpensive than cobalt, is used; lithium-nickel-cobalt-manganesecomposite oxide (LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂); lithium-manganesecomposite oxide (LiMn₂O₄), in which manganese is used; and the like.Among these, lithium-nickel-cobalt-manganese composite oxide has beenhighlighted as a material having excellent cycle characteristics andproviding high output with low resistance.

In order to achieve such good performance, it is required to use alithium composite oxide having a uniform particle diameter as a positiveelectrode active material.

The reason for this is that use of a composite oxide having a wideparticle size distribution causes unevenness of voltage applied toparticles in an electrode, whereby fine particles selectively degradewhen charge and discharge are repeated, and cycle deterioration iseasily caused. Therefore, in order to improve the performance of apositive electrode material, it is important to produce a lithiumcomposite oxide having a small and uniform particle diameter as apositive electrode active material.

In other words, a lithium composite oxide is usually produced from acomposite hydroxide, and therefore, in order to improve the performanceof a positive electrode material and produce a lithium-ion secondarybattery having high performance as a final product, a compositehydroxide including particles having a small particle diameter and anarrow particle size distribution needs to be used as a compositehydroxide to be used as a raw material of a lithium composite oxideconstituting a positive electrode material.

As for a particle size distribution of a lithium composite oxide, forexample, Japanese Patent Application Laid-Open No. 2008-147068 disclosesa lithium composite oxide, the lithium composite oxide being particleshaving a particle size distribution wherein, in a particle sizedistribution curve, an average particle diameter D50, which represents aparticle diameter having a cumulative frequency of 50%, is 3 to 15 μm, aminimum particle diameter is not less than 0.5 μm, and a maximumparticle diameter is not more than 50 μm, and furthermore, in arelationship between D50 and D10 as well as D50 and D90, the D10 havinga cumulative frequency of 10% and the D90 having a cumulative frequencyof 90%, D10/D50 and D10/D90 are 0.60 to 0.90 and 0.30 to 0.70,respectively. It is also disclosed that this lithium composite oxide hasa high density, is excellent in charge-and-discharge capacitycharacteristics and output characteristics, and is resistant todegradation even under heavy charge-and-discharge load conditions, andtherefore use of the lithium composite oxide allows a lithium ionnonaqueous electrolyte secondary battery having excellent outputcharacteristics and less degradation of cycle characteristics to beobtained.

However, the lithium composite oxide disclosed in Japanese PatentApplication Laid-Open No. 2008-147068 has an average particle diameterof 3 to 15 μm while having a minimum particle diameter of not less than0.5 μm and a maximum particle diameter of not more than 50 μm, and henceincludes very fine particles and coarse particles.

Moreover, it cannot be said that such particle size distributionspecified by the above-mentioned D10/D50 and D10/D90 is a narrowparticle size distribution.

In other words, it cannot be said that the lithium composite oxidedisclosed in Japanese Patent Application Laid-Open No. 2008-147068 isparticles having sufficiently high uniformity of particle diameters, andhence, even if such lithium composite oxide is adopted, improvement inperformance of a positive electrode material cannot be expected, and itis difficult to obtain a lithium ion nonaqueous electrolyte secondarybattery having sufficiently high performance.

Also, there has been proposed a method of producing a compositehydroxide to be used as a raw material of composite oxide, in order toimprove a particle size distribution. Japanese Patent ApplicationLaid-Open No. 2003-86182 proposes a method of producing a positiveelectrode active material for nonaqueous electrolyte batteries, whereinan alkaline solution is introduced together with an aqueous solutioncontaining two or more of transition metal salts or two kinds or more ofaqueous solutions of different transition metal salts into a reactionvessel to obtain a hydroxide or an oxide as a precursor throughcoprecipitation with a reductant being coexistent or an inert gas beingsupplied.

However, the technique disclosed in Japanese Patent ApplicationLaid-Open No. 2003-86182 aims to classify and collect formed crystals,and therefore, in order to obtain a product having a uniform particlediameter, production conditions need to be strictly controlled and it ishard to implement an industrial scale production. In addition, even ifcrystal particles having a large particle diameter can be obtained, itis difficult to obtain particles having a small particle diameter.

Further, in recent years, there have been made efforts to furtherimprove the performance by adding various elements. Tungsten acts toreduce reaction resistance, whereby the effect of achieving high-outputcan be expected. For example, Japanese Patent Application Laid-Open No.H11-16566 proposes a positive electrode active material which is coatedwith a metal containing at least one element selected from the groupconsisting of Ti, Al, Sn, Bi, Cu, Si, Ga, W, Zr, B, and Mo and/or anintermetallic compound obtained by a combination of a plurality of theabove mentioned elements, and/or an oxide. Japanese Patent ApplicationLaid-Open No. H11-16566 describes that such coating enables oxygen gasto be absorbed and safety to be secured, but does not disclose outputcharacteristics at all. Moreover, the disclosed manufacturing method iscoating using a planetary ball mill, and such coating method givesphysical damages to the positive electrode active material, and causesdecrease in battery characteristics.

Japanese Patent Application Laid-Open No. 2005-251716 proposes apositive electrode active material for nonaqueous electrolyte secondarybatteries, the positive electrode active material having at least alithium transition metal composite oxide having a layered structure,wherein the lithium transition metal composite oxide exists in aparticle form comprising either or both of primary particles andsecondary particles composed of aggregation of the primary particles,and has a compound comprising at least one element selected from thegroup consisting of molybdenum, vanadium, tungsten, boron, and fluorine,at least on the surface of said particles.

Thus, Japanese Patent Application Laid-Open No. 2005-251716 provides apositive electrode active material for nonaqueous electrolyte secondarybatteries, the positive electrode active material demonstratingexcellent battery characteristics even under severer environmentconditions for use, and particularly, describes the improvement ofinitial characteristics without loss of improvements in thermalstability, load characteristics, and output characteristics since thepositive electrode active material has, on the surface of the particles,a compound comprising at least one selected from the group consisting ofmolybdenum, vanadium, tungsten, boron, and fluorine.

However, Japanese Patent Application Laid-Open No. 2005-251716 describesthat the effect of at least one addition element selected from the groupconsisting of molybdenum, vanadium, tungsten, boron, and fluorine existsin improvement in initial characteristics, that is, initial dischargecapacity and initial efficiency, and thus it does not refer to outputcharacteristics. Also according to the disclosed manufacturing method,the addition element is mixed and burned with a hydroxide which has beenheat-treated simultaneously together with a lithium compound, andtherefore there is a problem that a part of the addition elementsubstitutes for nickel which has been arranged in layers, wherebybattery characteristics decrease.

In view of such problems, the present invention aims to provide atransition metal composite hydroxide, the use of which as a precursorallows a lithium transition metal composite oxide having a smallparticle diameter and high uniformity of particle diameters to beobtained.

Also, the present invention aims to provide a positive electrode activematerial for nonaqueous secondary batteries, the positive electrodeactive material being capable of reducing positive electrode resistancevalues measured when used for batteries, and also to provide anonaqueous electrolyte secondary battery including said positiveelectrode active material, the secondary battery having high capacityand thermal safety, and achieving high output.

Furthermore, the present invention aims to provide a method forindustrially producing the transition metal composite hydroxide and thepositive electrode active material according to the present invention.

SUMMARY OF THE INVENTION

The present inventors earnestly studied about a lithium transition metalcomposite oxide which can demonstrate excellent battery characteristicswhen used as a positive electrode material for a lithium-ion secondarybattery, and, as a result, they obtained a view that separation into anucleation stage and a particle growth stage by pH control incrystallization allows a particle size distribution of the transitionmetal composite hydroxide to be controlled. Also, the present inventorsobtained another view that a crystallized material is held in a slurryin which at least a tungsten compound is dissolved, and pH iscontrolled, whereby there is obtained a composite hydroxide on theparticle surface of which a tungsten-coated material is formed, and theuse of said composite hydroxide as a precursor allows a positiveelectrode active material capable of achieving high capacity and highoutput of a battery to be obtained. The present invention was completedbased on these views.

Specifically, a first aspect of the present invention is to provide amethod of producing a transition metal composite hydroxide, thetransition metal composite hydroxide being represented by a generalformula (1) MxWsAt(OH)2+α (wherein, x+s+t=1, 0<s≤0.05, 0<s+t≤0.15,0≤α≤0.5, M is at least one transition metal element selected from Ni, Coand Mn, and A is at least one additive element selected from transitionmetal elements other than M and W, group 2 elements, and group 13elements), being coated with a compound containing the additive element,and serving as a precursor of a positive electrode active material fornonaqueous electrolyte secondary batteries, the method comprising: acomposite hydroxide particle production step including a nucleationstage and a particle growth stage, the nucleation stage being such thata solution for nucleation containing a metal compound having an atomicratio of transition metals corresponding to an atomic ratio of M in thetransition metal composite hydroxide, and an ammonium ion supply sourceis controlled to have a pH of 12.0 to 14.0 at a reference solutiontemperature of 25 degrees C., whereby nuclei are formed, the particlegrowth stage being such that a solution for particle growth containingnuclei formed at the nucleation stage is controlled to have a pH of 10.5to 12.0 at a reference solution temperature of 25 degrees C. so as to belower than the pH at the nucleation stage, whereby the formed nuclei aregrown; and a coating step wherein composite hydroxide particles obtainedin the particle production step are mixed with a solution containing atleast a tungsten compound to make a slurry, and the slurry is controlledto have a pH of 7 to 9 at a reference solution temperature of 25 degreesC., whereby a coating material containing a metal oxide of tungsten andthe additive element or a metal hydroxide of tungsten and the additiveelement is formed on surfaces of the obtained composite hydroxideparticles.

A second aspect of the present invention is such that the additiveelement according to the first aspect is at least one element selectedfrom B, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, and Mo, and a third aspectof the present invention is such that the additive element preferablyincludes at least Al.

A fourth aspect of the present invention is such that the tungstencompound according to the first to third aspects is preferably either orboth of ammonium tungstate and sodium tungstate.

A fifth aspect of the present invention is characterized in that, in thecoating step according to the fourth aspect, the tungsten compound isammonium tungstate, and ammonia contained in a 25% ammonia solution inan amount equivalent to 0.5 to 25% by volume of an ammonium tungstatesaturated solution is added to the slurry.

A sixth aspect of the present invention is characterized in that, in thecoating step according to the third to fifth aspects, sodium aluminateis added to the slurry, and a seventh aspect of the present invention isto provide a method of producing a transition metal composite hydroxide,wherein, in the coating step according to the sixth aspect, pH iscontrolled by adding a sulfuric acid to the slurry thereby toprecipitate a tungsten compound and an aluminum compound simultaneouslyand to coat a surface of the composite hydroxide.

An eighth aspect of the present invention is to provide a transitionmetal composite hydroxide represented by a general formula (1)MxWsAt(OH)2+α (wherein, x+s+t=1, 0<s≤0.05, 0<s+t≤0.15, 0≤α≤0.5, M is atleast one transition metal selected from Ni, Co and Mn, and A is atleast one additive element selected from transition metal elements otherthan M and W, group 2 elements, and group 13 elements) and serving as aprecursor of a positive electrode active material for nonaqueouselectrolyte secondary batteries, wherein the transition metal compositehydroxide is secondary particles having a substantially spherical shapeand composed of aggregation of a plurality of primary particles, thesecondary particles have an average particle diameter of 3 to 7 μm andan index indicating a scale of particle-size distribution,[(d90−d10)/average-particle-diameter], of not more than 0.55, and acoating material containing a metal oxide of tungsten and the additiveelement or a metal hydroxide of tungsten and the additive element isformed on surfaces of the secondary particles.

A ninth aspect of the present invention is characterized in that thetransition metal composite hydroxide according to the eighth aspect hasa specific surface area of 5 to 30 m2/g.

A tenth aspect of the present invention is characterized in that theadditive element according to the eighth and ninth aspects is at leastone element selected from B, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, andMo, and an eleventh aspect of the present invention is to provide atransition metal composite hydroxide, wherein s+t in the general formula(1) according to the eighth to tenth aspects is 0.02<s+t≤0.15.

A twelfth aspect of the present invention is to provide a transitionmetal composite hydroxide, wherein the coating material according to thetenth to eleventh aspects is a mixture containing a tungsten oxidehydrate and an aluminum hydroxide.

A thirteenth aspect of the present invention is to provide a method ofproducing a positive electrode active material for nonaqueouselectrolyte secondary batteries, the positive electrode active materialcomprising a lithium transition metal composite oxide represented by ageneral formula (2) Li1+uMxWsAtO2 (wherein, −0.05≤u≤0.50, x+s+t=1,0<s≤0.05, 0<s+t≤0.15, M is at least one transition metal selected fromNi, Co and Mn, and A is at least one additive element selected fromtransition metal elements other than M and W, group 2 elements, andgroup 13 elements) and having a layered hexagonal crystal structure, themethod comprising: a hydroxide particle production step of obtaining atransition metal composite hydroxide by the production method accordingto any one of the first to fourth aspect; a mixing step of mixing thetransition metal composite hydroxide with a lithium compound to form alithium mixture; and a burning step of burning the lithium mixtureformed in the mixing step under an oxidizing atmosphere at a temperatureof 700 to 1000 degrees C.

A fourteenth aspect of the present invention is to provide a method ofproducing a positive electrode active material for nonaqueouselectrolyte secondary batteries, wherein the lithium mixture accordingto the thirteenth aspect is adjusted so that a ratio of a total numberof atoms of metals contained in the lithium mixture other than lithiumto the number of atoms of lithium contained therein is 1:0.95 to 1:1.5.

A fifteenth aspect of the present invention is to provide a method ofproducing a positive electrode active material for nonaqueouselectrolyte secondary batteries, wherein, in the burning step accordingto the thirteenth aspect, calcination is performed in advance at atemperature of 350 to 800 degrees C.

A sixteenth aspect of the present invention is to provide a positiveelectrode active material for nonaqueous electrolyte secondarybatteries, the positive electrode active material comprising a lithiumtransition metal composite oxide represented by a general formula (2)Li1+uMxWsAtO2 (wherein, −0.05≤u≤0.50, x+s+t=1, 0<s≤0.05, 0<s+t≤0.15, Mis at least one transition metal selected from Ni, Co and Mn, and A isat least one additive element selected from transition metal elementsother than M and W, group 2 elements, and group 13 elements) and havinga layered hexagonal crystal structure, wherein the positive electrodeactive material has an average particle diameter of 3 to 8 μm and anindex indicating a scale of particle-size distribution,[(d90−d10)/average-particle-diameter], of not more than 0.60.

A seventeenth aspect of the present invention is characterized in thatthe positive electrode active material for nonaqueous electrolytesecondary batteries according to the sixteenth aspect has a specificsurface area of 0.5 to 2.0 m2/g.

An eighteenth aspect of the present invention is to provide a positiveelectrode active material for nonaqueous electrolyte secondarybatteries, wherein the additive element according to the sixteenth andseventeenth aspects is at least one element selected from B, Al, Sc, Y,Ti, Zr, Hf, V, Nb, Ta, Cr, and Mo, and furthermore, according to anineteenth aspect of the present invention, the additive elementpreferably includes at least Al.

A twentieth aspect of the present invention is to provide a positiveelectrode active material for nonaqueous electrolyte secondarybatteries, wherein M in the general formula (2) according to thesixteenth to nineteenth aspects includes at least Ni and Co, and atwenty-first aspect of the present invention is to provide a positiveelectrode active material for nonaqueous electrolyte secondarybatteries, wherein M in the general formula (2) according to thesixteenth to nineteenth aspects includes at least Ni and Mn.

A twenty-second aspect of the present invention is to provide a positiveelectrode active material for nonaqueous electrolyte secondarybatteries, wherein s+t in the general formula (2) according to thesixteenth to nineteenth aspects is 0.02<s+t≤0.15.

A twenty-third aspect of the present invention is to provide anonaqueous electrolyte secondary battery, wherein a positive electrodeis formed of the positive electrode active material for nonaqueouselectrolyte secondary batteries according to the sixteenth totwenty-second aspects.

Advantageous Effects of Invention

According to the present invention, a monodisperese transition metalcomposite hydroxide having a small particle diameter and a narrowparticle size distribution can be obtained, and a positive electrodeactive material which comprises a lithium transition metal compositeoxide and obtained in the case where the obtained transition metalcomposite hydroxide is used as a precursor is capable of achieving anonaqueous secondary battery having high-capacity, high temperaturestability, and high-output, and a nonaqueous electrolyte secondarybattery composed of a positive electrode including said positiveelectrode active material can have excellent battery characteristics.

The method of producing a transition metal composite hydroxide and themethod of producing a positive electrode active material according tothe present invention each are easy and suitable for industrial scalemanufacturing, and accordingly have a great industrial value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic flow chart illustrating a process of producing atransition metal composite hydroxide according to the present invention.

FIG. 2 is a schematic flow chart illustrating another process ofproducing a transition metal composite hydroxide according to thepresent invention.

FIG. 3 is a schematic flow chart illustrating a process of producing alithium transition metal composite oxide from a transition metalcomposite hydroxide according to the present invention.

FIG. 4 is a schematic flow chart illustrating a flow from producing atransition metal composite hydroxide to producing a nonaqueouselectrolyte secondary battery according to the present invention.

FIG. 5 is a schematic sectional view of a coin-type battery B used forbattery evaluation.

FIG. 6 illustrates a measurement example of alternating currentimpedance evaluation and an equivalent circuit used for analysis.

FIG. 7 is a FE-SEM photograph of a lithium transition metal compositehydroxide (positive electrode active material) according to the presentinvention (at an observation magnification of 1,000×).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to the following inventions.

1. A transition metal composite hydroxide which serves as a precursor ofa positive electrode active material for nonaqueous electrolytesecondary batteries, and a method of producing the same.

2. A positive electrode active material for nonaqueous electrolytesecondary batteries, the positive electrode active material includingthe transition metal composite hydroxide described in theabove-mentioned invention 1, and a method of producing the positiveelectrode active material.

3. A nonaqueous electrolyte secondary battery formed using the positiveelectrode active material described in the above-mentioned invention 2.

Hereinafter, the above-mentioned inventions 1 to 3 will be explained indetail, namely, (1) a transition metal composite hydroxide and a methodof producing the same will be explained first, and then, (2) a positiveelectrode active material for nonaqueous electrolyte secondarybatteries, the positive electrode active material using the transitionmetal composite hydroxide as a precursor, and a method of producing thepositive electrode active material, and lastly, (3) a nonaqueouselectrolyte secondary battery as a final product will be explained.

1-1. Transition Metal Composite Hydroxide

A transition metal composite hydroxide according to the presentinvention (hereinafter, simply referred to as composite hydroxideaccording to the present invention) is represented by a general formula(1) MxWsAt(OH)2+α (wherein, x+s+t=1, 0<s≤0.05, 0<s+t≤0.15, 0≤α≤0.5, M isat least one transition metal selected from Ni, Co and Mn, and A is atleast one additive element selected from transition metal elements otherthan M and W, group 2 elements, and group 13 elements) and is secondaryparticles having a substantially spherical shape and composed ofaggregation of a plurality of primary particles, wherein the secondaryparticles have an average particle diameter of 3 to 7 μm and an indexindicating a scale of particle-size distribution,[(d₉₀−d₁₀)/average-particle-diameter], of not more than 0.55, and acoating material containing a metal oxide of tungsten and the additiveelement or a metal hydroxide of tungsten and the additive element isformed on surfaces of the secondary particles.

The composite hydroxide according to the present invention isparticularly suitable as a precursor of the positive electrode activematerial according to the present invention.

Hereinafter, an explanation will be given based on the premise that thecomposite hydroxide is used as a precursor of the positive electrodeactive material according to the present invention.

[Particle Structure]

The composite hydroxide according to the present invention is adjustedso as to comprise substantially-spherical-shaped particles, specificallysecondary particles having a substantially spherical shape and composedof aggregation of a plurality of primary particles. Such a structureallows lithium to be sufficiently diffused into the particles in asintering process for forming a positive electrode active materialaccording to the present invention, whereby a positive electrode activematerial having a uniform and good distribution of lithium is formed.

Furthermore, it is more preferable that the primary particles areaggregated in a random direction to form secondary particles.

The aggregation of the primary particles in a random direction allowsvoids to be formed almost uniformly between the primary particles, andtherefore, when the secondary particles are mixed with a lithiumcompound and burned, the melted lithium compound spreads into thesecondary particles, and lithium is thus sufficiently diffused.

[Particle Size Distribution]

The composite hydroxide according to the present invention is adjustedso as to have an index indicating a scale of particle-size distribution,[(d90−d10)/average-particle-diameter], of not more than 0.55.

A particle size distribution of a positive electrode active material isstrongly affected by a raw material, that is, a composite hydroxide, andtherefore, in the case where fine particles or coarse particles aremixed in the composite hydroxide, then the positive electrode activematerial also includes the same type of particles.

In other words, if a composite hydroxide has[(d90−d10)/average-particle-diameter] of more than 0.55 to become awider particle size distribution, then a positive electrode activematerial also includes fine particles or coarse particles.

Also, in the case where a positive electrode is formed using a positiveelectrode active material including many fine particles, a localreaction of the fine particles may cause heat generation, andaccordingly safety is lowered and also the fine particles areselectively degraded, whereby cycle characteristics are worsened.

On the other hand, in the case where a positive electrode is formedusing a positive electrode active material including many particleshaving a large diameter, a reaction area of an electrolyte solution withthe positive electrode active material cannot be sufficiently secured,whereby an increase in reaction resistance causes a decrease in batteryoutput.

By the adjustment of the composite hydroxide according to the presentinvention so as to have an index [(d90−d10)/average-particle-diameter]of not more than 0.55, a positive electrode active material obtained byusing the composite hydroxide according to the present invention as araw material also have a narrower range of a particle size distributionand have a uniform particle diameter.

In other words, a positive electrode active material to be obtained canhave an index [(d₉₀−d₁₀)/average-particle-diameter] of not more than 0.6in a particle size distribution thereof. Thus, a battery which has anelectrode formed with the positive electrode active material obtainedusing the composite hydroxide according to the present invention as araw material is allowed to have good cycle characteristics andhigh-output.

Here, it may be considered that composite hydroxide particles having awide normal-distribution are classified to obtain a composite hydroxidehaving a narrower particle-size distribution, but there is no sievehaving an opening capable of being used for particles having the samelevel of average particle diameter as that of the composite hydroxideparticles according to the present invention, and thus classificationusing a sieve is difficult. Also, even using an apparatus such as a wetcyclone, the particles cannot be classified so as to have a sufficientlynarrow particle-size distribution, and thus it is difficult to obtain acomposite hydroxide having a uniform particle diameter and a narrowparticle-size distribution, by an industrial classification method.

As an example, using a cylinder type reaction vessel equipped with astirrer and a overflow pipe, a mixed solution of nickel sulfate andcobalt sulfate of a composition ratio, and aqueous ammonia were added tothe reaction vessel, whereby pH was controlled to 11.5 to 12.0, andafter a state inside the reaction vessel became stationary, compositehydroxide particles having a composition of Ni0.85Co0.15(OH)2 werecontinuously collected from the overflow pipe. Using a wet cyclone(hydrocyclone, NHC-1, manufactured by Japan Chemical Engineering &Machinery Co., Ltd.), supply pressure was increased to remove coarsepowder from the obtained composite hydroxide particles, and then thesupply pressure was reduced to remove fine particles therefrom. However,only composite hydroxide particles having an average particle diameterof 6.5 and [(d90−d10)/average-particle-diameter] of 0.65 were obtained.

Note that, in an index indicating a scale of a particle-sizedistribution, that is, [(d90−d10)/average-particle-diameter], d10represents a particle diameter obtained at the point in time when thenumber of particles in each particle diameter is accumulated in theorder from small particle diameter and an accumulated volume thereofreaches 10% of a total volume of all the particles. On the other hand,d90 represents a particle diameter obtained at the point in time whenthe number of particles is accumulated in the same way as mentionedabove and an accumulated volume thereof reaches 90% of a total volume ofall the particles.

Methods of calculating an average particle diameter (d50), d90, and d10are not particularly limited, but, for example, they can be obtainedfrom an integrated value of volume measured with a laser diffractionscattering type particle-size analyzer.

[Average Particle Diameter]

The composite hydroxide according to the present invention is adjustedto have an average particle diameter of 3 to 7 μm.

By the adjustment of the average particle diameter to 3 to 7 μm, apositive electrode active material formed using the composite hydroxideaccording to the present invention as a precursor also can be adjustedto have a predetermined average particle diameter (3 to 8 μm), whereby adesirable positive electrode active material can be formed.

Here, in the case where the composite hydroxide has an average particlediameter of less than 3 μm, the positive electrode active materialformed also has a small average particle diameter, and filling densityin a positive electrode is lowered, whereby a battery capacity pervolume is reduced. In addition, the positive electrode active materialsometimes has a too large specific surface area. On the other hand, inthe case where the composite hydroxide has an average particle diameterof more than 7 μm, a specific surface area of the positive electrodeactive material is decreased to reduce an interface with an electrolytesolution, whereby resistance of a positive electrode is increased tocause reduction in output characteristics of a battery.

Therefore, the composite hydroxide according to the present invention isadjusted to have an average particle diameter of 3 to 7 um, and usingthis adjusted composite hydroxide as a raw material, the positiveelectrode active material according to the present invention can beformed, and when a positive electrode using this positive electrodeactive material is applied to a battery, excellent batterycharacteristics can be achieved.

[Specific Surface Area]

The composite hydroxide according to the present invention is adjustedto have a specific surface area of 5 to 30 m2/g.

The control of said specific surface area of 5 to 30 m2/g allows apositive electrode active material formed using the composite hydroxideaccording to the present invention as a precursor to have apredetermined specific surface area (0.5 to 2.0 m2/g).

Here, in the case where the composite hydroxide has a specific surfacearea of less than 5 m2/g, the positive electrode active material formedhas a small specific surface area, and accordingly, not only outputcharacteristics of a battery are sometimes reduced, but also a reactionin burning after mixing with a lithium compound sometimes insufficientlyproceeds.

On the other hand, in the case where the composite hydroxide has aspecific surface area of more than 30 m2/g, the positive electrodeactive material has a too large specific surface area, and accordingly,not only heat stability of the positive electrode active material issometimes lowered, but also sintering of the particles in the burningproceeds, whereby coarse particles are sometimes formed.

[Composition of Composite Hydroxide]

The composite hydroxide according to the present invention is adjustedto have a composition expressed by a general formula (1) shown below.

In the case where a lithium transition metal composite oxide is producedusing the composite hydroxide having such composition as a precursor,when an electrode using this lithium transition metal composite oxide asa positive electrode active material is applied to a battery, a value ofpositive electrode resistance to be measured can be made lower and goodoutput characteristics of a battery can be achieved.[Chemical Formula 1]M_(x)W_(s)A_(t)(OH)_(2+α)  (1)

wherein,

x+s+t=1, 0<s≤0.05, 0<s+t≤0.15, 0≤α≤0.5,

M is at least one transition metal selected from Ni, Co and Mn, and

A is at least one additive element selected from transition metalelements other than M and W, group 2 elements, and group 13 elements.

The composite hydroxide according to the present invention may have acomposition capable to be a precursor of a lithium transition metalcomposite oxide, but specifically, the composite hydroxide representedby the following general formula (1-1) or (1-2) is preferable.[Chemical Formula 2]Ni_(1-x-s-t)Co_(x)W_(s)A_(t)(OH)_(2+α)  (1-1)

wherein,

0≤x≤0.2, 0<s≤0.05, 0<s+t≤0.15, x+s+t<0.3, 0≤α≤0.5, and

A is at least one additive element selected from transition metalelements other than Ni, Co and W, group 2 elements, and group 13elements.[Chemical Formula 3]Ni_(x)Mn_(y)Co_(z)W_(s)A_(t)(OH)_(2+α)  (1-2)

wherein,

x+y+z+s+t=1, 0.3≤x≤0.7, 0.1≤y≤0.55, 0≤z≤0.4, 0<s≤0.05, 0<s+t≤0.15,0≤α≤0.5, and

A is at least one additive element selected from transition metalelements other than Ni, Co, Mn and W, group 2 elements, and group 13elements.

In the case where a positive electrode active material is obtained byusing the above-mentioned composite hydroxide as a precursor, thepositive electrode active material comes to have the same compositionratio as that of the composite hydroxide. Therefore, the compositehydroxide according to the present invention is adjusted so as to havethe same composition ratio as that of the positive electrode activematerial to be obtained.

[Particle Structure]

In the composite hydroxide according to the present invention, a coatingmaterial containing a metal oxide of tungsten and the additive elementor a metal hydroxide of tungsten and the additive element is formed onsurfaces of the composite hydroxide particles.

Thus, a positive electrode active material can be mase to containtungsten and an additive element uniformly. If it is aimed to make apositive electrode active material contain tungsten and an additiveelement, it may be enough only to partially form a coating material onthe surfaces of composite hydroxide particles, but, in order to controlvariation of amounts of tungsten and the additive element contained ineach particle of a positive electrode active material, it is preferableto make a coating material uniformly adhere to surfaces of compositehydroxide particles and thereby to form a thin coating layer.

Furthermore, in the case where a total amount of tungsten and anadditive element contained is small, a coating layer may be formed as ametal oxide or a metal hydroxide in which a transition metal containedas M in the above-mentioned general formula (1) is mixed with tungstenand the additive element.

Thus, even if an amount of tungsten and an additive element is small, acontent thereof in each particle can be controlled to be uniform.

Also, in the case where aluminum is selected as an additive element inorder to improve thermal stability, the coating material is preferably amixture containing tungsten oxide hydrate and aluminum hydroxide. Thus,a synergic effect of tungsten and aluminum makes it possible to improveoutput characteristics and thermal stability of a battery.

1-2. Method of Producing Transition Metal Composite Hydroxide

The composite hydroxide according to the present invention having theabove-mentioned characteristics is produced by the following method.

The method of producing the composite hydroxide according to the presentinvention is such that a coating material containing tungsten and anadditive element is formed on the surfaces of transition metal compositehydroxide particles obtained by a crystallization reaction, whereby thecomposite hydroxide is produced, the method comprising:

(A) a composite hydroxide particle production step including

(A-1) a nucleation stage of performing nucleation and

(A-2) a particle growth stage of growing up a nucleus formed at thenucleation stage; and

(B) a coating step of forming a coating material containing a metaloxide of tungsten and the additive element or a metal hydroxide oftungsten and the additive element on the surfaces of said compositehydroxide particles.

In other words, in a continuous crystallization method of the prior art,a nucleation reaction and a particle growth reaction proceed in the samevessel at the same time, whereby a particle size distribution range iswider. On the other hand, the method of producing a composite hydroxideaccording to the present invention is to clearly separate a time when anucleation reaction mainly occurs (nucleation step) from a time when aparticle growth reaction mainly occurs (particle growth step), therebyachieving a narrow particle size distribution.

Furthermore, the method is characterized in that a coating materialcontaining a metal oxide of tungsten and the additive element or a metalhydroxide of tungsten and the additive element is formed uniformly onthe surfaces of the composite hydroxide particles obtained in theparticle production step.

First, an outline about the production method of the composite hydroxideaccording to the present invention will be explained based on FIG. 1.Note that, in FIG. 1 and FIG. 2, the combination of (A-1) the nucleationstage and (A-2) the particle growth stage corresponds to (A) thecomposite hydroxide particle production step.

(A) Composite Hydroxide Particle Production Step

(A-1) Nucleation Stage

As illustrated in FIG. 1, first, a plurality of metal compoundscontaining at least one transition metal selected from Ni, Co, and Mn isdissolved in water at a predetermined ratio to produce a mixed solution.In the method of producing a composite hydroxide according to thepresent invention, a metal composition ratio in the composite hydroxideparticles obtained is the same as the metal composition ratio in themixed solution. Therefore, the metal ratio of the metal compounds to bedissolved in water is adjusted so that the mixed solution has the samemetal composition ratio as the composite hydroxide according to thepresent invention, whereby this mixed solution is produced.

On the other hand, an alkaline solution, such as a sodium hydroxidesolution, an ammonia solution containing an ammonium ion supply source,and water are fed into a reaction vessel and mixed to form a solution.

Such a solution (hereinafter referred to as a pre-reaction solution) isadjusted to have a pH of 12.0 to 14.0 at a reference solutiontemperature of 25 degrees C. after adjustment of a feeding amount of thealkaline solution. In addition, the pre-reaction solution is adjusted tohave an ammonium ion concentration of 3 to 25 g/L. Furthermore, thepre-reaction solution is adjusted to have a temperature of 20 to 60degrees C. Note that the pH value and the ammonium ion concentration ofthe solution in the reaction vessel are measured by a common pH meterand a common ion meter, respectively.

Then, after adjusting the temperature and the pH value of thepre-reaction solution, with the pre-reaction solution being stirred, themixed solution is fed into the reaction vessel. Thus, a solution(hereinafter referred to as a reaction solution) obtained by mixing thepre-reaction solution with the mixed solution is formed in the reactionvessel, whereby very fine nuclei of composite hydroxide particlesaccording to the present invention can be formed in the reactionsolution. At this time, the reaction solution has a pH value in theabove-mentioned range, and therefore the formed nuclei hardly grow, andnucleation occurs on a priority basis.

Note that as the nucleation by feeding the mixed solution proceeds, thepH value and the ammonium ion concentration of the reaction solutionvary, and therefore, besides the mixed solution, the alkaline solutionand the ammonia solution are fed into the reaction solution, whereby thereaction solution is controlled so that the pH value and the ammoniumion concentration of the reaction solution each are maintained at thecorresponding predetermined value.

Thus, the feeding of the mixed solution, the alkaline solution, and theammonia solution into the reaction solution allows a new nucleus to beformed continuously in the reaction solution. Then, when a predeterminedamount of nuclei is formed in the reaction solution, the nucleationstage is completed. Whether the predetermined amount of nuclei is formedor not is determined with an amount of metal salt added to the reactionsolution.

This reaction solution, that is, a solution being obtained by mixing themixed solution with the alkaline solution and the ammonia solution andbeing adjusted to have a pH of 12.0 to 14.0, is a claimed solution fornucleation.

(A-2) Particle Growth Stage

After completion of the nucleation stage, the reaction solution isadjusted so as to have a pH value lower than the pH value at thenucleation stage within a pH range of 10.5 to 12.0 at a referencesolution temperature of 25 degrees C. Specifically, the pH value of thereaction solution is controlled by adjusting a feeding amount of thealkaline solution.

When the pH value of the reaction solution is controlled to be withinthe above-mentioned range, the nuclear growth reaction occurs on apriority basis to the nucleation reaction, and therefore a new nucleusis hardly formed in the reaction solution, whereas nuclei grow to formcomposite hydroxide particles according to the present invention havinga predetermined particle diameter.

After that, at the time when the composite hydroxide particles grow tohave the predetermined particle diameter, the particle growth stage iscompleted. By finding a relationship between an amount of metal saltadded to the reaction solution at the nucleation stage and the particlegrowth stage and the obtained particles from the preliminary testresults, the particle diameter of the composite hydroxide particles canbe easily determined.

Such a reaction solution, that is, a solution being obtained by mixingthe mixed solution with the alkaline solution and the ammonia solutionand being adjusted to have a pH of 10.5 to 12.0, is a claimed solutionfor particle growth.

As mentioned above, in the composite hydroxide particle production step,at the nucleation stage, the nucleation occurs on a priority basiswhereas the nuclear growth hardly occurs, on the other hand, at theparticle growth stage, only the nucleus growth occurs while a newnucleus is hardly formed.

Thus, at the nucleation stage, nuclei having a narrow particle sizedistribution and being homogeneous can be formed, on the other hand, atthe particle growth stage, nuclei can be grown homogeneously. Therefore,in the composite hydroxide particle production step, composite hydroxideparticles having a narrow particle size distribution and beinghomogeneous can be obtained.

Note that, in the above-mentioned production step, metal ions arecrystallized out as nuclei or composite hydroxide particles at both thestages, whereby a ratio of a liquid component to a metal component inthe reaction solution is increased. When this liquid component isincreased, seemingly, a concentration of the mixed solution to be fed isdecreased, and thus, there is a possibility that composite hydroxideparticles are not sufficiently grow at the particle growth stage.

Therefore, in order to control an increase in the above-mentioned liquidcomponent, a part of the liquid component in the reaction solution needsto be discharged out of the reaction vessel after completion of thenucleation stage or during the particle growth stage.

Specifically, the feeding of the mixed solution and the like into thereaction solution and stirring is stopped thereby to precipitate nucleiand composite hydroxide particles, and a supernatant liquid of thereaction solution is discharged.

Thus, a relative concentration of the mixed solution in the reactionsolution can be made higher, and composite hydroxide particles can begrown in a state where a relative concentration of the mixed solution ishigh, whereby a particle-size distribution of the composite hydroxideparticles can be further narrowed and a particle density of thecomposite hydroxide particles in the secondary particles can also bemade higher.

Also, in the above-mentioned embodiment, the pH value of the solutionfor nucleation obtained after completion of the nucleation stage isadjusted to form the solution for the particle growth, and the particlegrowth is performed immediately after the nucleation stage, andtherefore there is an advantage that shift to the particle growth stagecan be performed quickly.

Furthermore, there are advantages that the shift from the nucleationstage to the particle growth stage can be performed only by adjustmentof the pH of the reaction solution and this pH adjustment can be easilyperformed by temporarily stopping the feeding of the alkaline solution.Note that the pH of the reaction solution can be adjusted by addinginorganic acid which is the same kind of acid constituting the metalcompound, for example, sulfuric acid in the case of sulfate, to areaction solution.

Alternatively, as shown in FIG. 2, there may be another embodimentwherein, aside from a solution for nucleation, a component-adjustedsolution adjusted to have a pH value and an ammonium ion concentrationsuitable for the nucleation stage is formed, and a solution containingnuclei formed in another reaction vessel by performing a nucleationprocess is added to this component-adjusted solution thereby to producea reaction solution, and a particle growth process is performed for thisreaction solution (that is, a solution for particle growth).

In this case, since the nucleation stage and the particle growth stagecan be separated surely, a state of the reaction solution in each of theprocesses can be adjusted to be optimum for each of the processes.Particularly, the reaction solution can be adjusted to have an optimalpH condition from the initial stage of the particle growth stage.Therefore, the composite hydroxide particles formed at the particlegrowth stage can be made to have a narrower particle-size distributionand to be uniform.

Next, materials, solutions, and reaction conditions which are used ateach of the stages will be explained in detail.

[pH Value]

(Nucleation Stage)

At the nucleation stage, the reaction solution is controlled so as tohave a pH value of 12.0 to 14.0, preferably 12.5 to 13.0 at a referencesolution temperature of 25 degrees C.

When a pH value is more than 14.0, produced nuclei are too minute,whereby a problem that the reaction solution is gelled arises. On theother hand, when the pH value is less than 12.0, a nucleus growthreaction occurs as well as a nucleation reaction, and thus formed nucleihave a wider particle-size distribution and are non-uniform.

Therefore, the reaction solution at the nucleation step needs to have apH value of 12.0 to 14.0, and such pH value range makes it possible tocontrol nucleus growth at the nucleation step, whereby almost onlynucleation can be induced, and formed nuclei can be uniform and have anarrower particle-size distribution.

(Particle Growth Stage)

At the particle growth stage, the reaction solution is controlled so asto have a pH value of 10.5 to 12.0, preferably 11.0 to 12.0 at areference solution temperature of 25 degrees C.

When the pH value is more than 12.0, too many nuclei are newly formedand accordingly hydroxide particles having a good particle sizedistribution cannot be obtained.

On the other hand, when the pH value is less than 10.5, solubility dueto ammonia ions is high and more metal ions remain in the solutionwithout precipitating, whereby production efficiency is worsened. Also,in the case where metal sulfate is used as a raw material, a more amountof S (sulfur) remains in the particles.

Therefore, the reaction solution at the particle growth step needs tohave a pH value of 10.5 to 12.0, and such pH value makes it possible toinduce only growth of nuclei formed at the nucleation on a prioritybasis and to control formation of a new nucleus, whereby compositehydroxide particles obtained can be uniform and have a narrowerparticle-size distribution.

At both the nucleation stage and the particle growth stage, it ispreferable that a pH value fluctuation range is within plus and minus0.2 of a predetermined value. When the pH value fluctuation range iswider, the nucleation and the particle growth are not stable andaccordingly sometimes composite hydroxide particles having a narrowrange of particle size distribution and being uniform cannot beobtained.

Note that, since the pH value of 12 is a boundary condition between thenucleation and the nucleus growth, depending on presence or non-presenceof nuclei in the reaction solution, said pH value can be used as acondition for either the nucleation process or the particle growthprocess.

That is, in the case where a pH value at the nucleation stage is set tohigher than 12 to form a large amount of nuclei and then, at theparticle growth stage, the pH value is set to 12, a large amount ofnuclei comes to be present in the reaction solution, and accordinglynucleus growth occurs on a priority basis, whereby hydroxide particleshaving a narrow particle-size distribution and a comparatively largeparticle diameter can be obtained.

On the other hand, in the case where no nucleus is present in thereaction solution, that is, a pH is set to 12 at the nucleation stage,no nucleus to grow is present, and accordingly nucleation occurs on apriority basis, and a pH value at the particle growth stage is set toless than 12, formed nuclei grow, whereby the above-mentioned hydroxideparticles having a good quality can be obtained.

In each of the cases, a pH value at the particle growth stage just needsto be controlled to be lower than a pH at the nucleation stage.

[Formation Amount of Nucleus]

An amount of nuclei formed at the nucleation stage is not particularlylimited, but, in order to obtain composite hydroxide particles having agood particle size distribution, preferably 0.1 to 2% of the wholeamount, that is, all the metal salts supplied in order to obtaincomposite hydroxide particles, more preferably not more than 1.5%.

[Particle Diameter Control of Composite Hydroxide Particles]

A particle diameter of composite hydroxide according to the presentinvention hardly changes in the coating step, and therefore control of aparticle diameter of the particles in the composite hydroxide particleproduction step allows a desired particle diameter to be obtained. Theparticle diameter of the above-mentioned composite hydroxide particlescan be controlled using a time of the particle growth stage, andtherefore, when the particle growth stage is continued until thecomposite hydroxide particles grow to have a desired particle diameter,the compound hydroxide particles having a desired particle diameter canbe obtained.

Also, a particle diameter of the composite hydroxide particles can becontrolled not only at the particle growth stage but also by a pH valueat the nucleation stage and an amount of a raw material fed for thenucleation.

In other words, by setting a pH value in the nucleation at the high pHside or by making a nucleation time longer, an amount of a raw materialto be fed is increased and the number of nuclei formed is increased.Thus, even when the particle growth step is performed under the sameconditions, the composite hydroxide particles can be made to have asmaller particle diameter.

On the other hand, when the number of nuclei formed is controlled so asto be less, the composite hydroxide particles having a larger particlediameter can be obtained.

Hereinafter, conditions, such as a metal compound, an ammoniaconcentration in the reaction solution, a reaction temperature, anatmosphere, and the like will be explained. The difference in conditionsbetween the nucleation stage and the particle growth stage is only acontrol range of a pH value of the reaction solution, and conditions,such as a metal compound, an ammonia concentration in the reactionsolution, a reaction temperature, and an atmosphere are substantiallythe same at both the stages.

[Metal Compound]

A compound containing target metal is used as a metal compound.

A water-soluble compound is preferably used as the compound, andexamples of said compound include nitrate, sulfate, and hydrochloride.For example, nickel sulfate, cobalt sulfate, or manganese sulfate ispreferably used.

[Additive Element]

As an additive element (at least one additive element selected fromtransition metal elements other than M and W, group 2 elements, andgroup 13 elements), a water-soluble compound is preferably used. Forexample, aluminum sulfate, titanium sulfate, ammonium peroxotitanate,potassium titanium oxalate, vanadium sulfate, ammonium vanadate,chromium sulfate, potassium chromate, zirconium sulfate, zirconiumnitrate, niobium oxalate, ammonium molybdate, or the like may be used.

To uniformly disperse said additive element inside the compositehydroxide particles, an additive containing the additive element justneeds to be added to the mixed solution, whereby, in a state where theadditive element is uniformly dispersed inside the composite hydroxideparticles, coprecipitation thereof can be performed.

[Concentration of Mixed Solution]

The mixed solution preferably has a total metal compound concentrationof 1 to 2.6 mol/L. In the case where the mixed solution has theconcentration of less than 1 mol/L, an amount of precipitate perreaction vessel is smaller and thereby productivity is reduced, which isnot preferable.

On the other hand, in the case where the mixed solution has a saltconcentration of more than 2.6 mol/L, the concentration exceeds asaturated concentration of the solution when a liquid temperature falls,whereby a crystal re-precipitates and thereby causes a risk, such asblocking of equipment piping.

The metal compound may not be necessarily fed into a reaction vessel ina form of a mixed solution, and for example, in the case where a metalcompound which reacts to form a compound when mixed is used, metalcompound solutions may be individually prepared so as to have a totalconcentration of all the metal compound solutions within theabove-mentioned concentration range, and simultaneously fed into areaction vessel at a predetermined ratio as individual metal compoundsolutions.

Furthermore, it is preferable that the mixed solution and the like andeach metal compound solution are fed into a reaction vessel in theamounts in which a concentration of a crystallized product isapproximately 30 to 200 g/L at the time of completion of crystallizationreaction. This is because when a concentration of the crystallizedproduct is less than 30 g/L, aggregation of primary particles issometimes insufficient, on the other hand, when a concentration of thecrystallized product is more than 200 g/L, the mixed solution addedinsufficiently diffuses into the reaction vessel and accordingly animbalance in particle growth is sometimes caused.

[Ammonia Concentration]

A concentration of ammonia in the reaction solution is preferablymaintained at a fixed value within a range of 3 to 25 g/L.

Ammonia acts as a complexing agent, and therefore, when a concentrationof ammonia is less than 3 g/L, the solubility of metal ions cannot bemaintained constant, plate-like hydroxide primary particles which areuniform in shape and particle diameter are not formed, and gel-likenuclei are easily formed, whereby a particle size distribution is easilymade wider.

On the other hand, the ammonia concentration of more than 25 g/L causestoo high solubility of metal ions and an increase in amount of metalions remaining in the reaction solution, whereby deviation incomposition is caused. Moreover, crystallinity of the particles becomeshigh, whereby a specific surface area is sometimes too small.

Furthermore, when the ammonia concentration varies, the solubility ofmetal ions varies and uniform hydroxide particles are not formed, andtherefore the ammonia concentration is preferably maintained at a fixedvalue. For example, the ammonia concentration is preferably maintainedat a desired concentration in a range between upper and lower limits ofapproximately 5 g/L.

Note that an ammonium ion supply source is not particularly limited,but, for example, ammonia, ammonium sulfate, ammonium chloride, ammoniumcarbonate, ammonium fluoride, or the like may be used.

[Reaction Atmosphere]

At the nucleation stage, in view of controlling oxidation of transitionmetal, particularly cobalt and manganese, to stably form particles, aconcentration of oxygen in a space inside the reaction vessel ispreferably controlled to not more than 10% by volume, more preferablynot more than 5% by volume, and also it is preferable that, with aconcentration of oxygen dissolved in a solution in the reaction vesselbeing controlled to not more than 2 mg/L, a crystallization reaction isperformed. This manner allows unnecessary oxidation of particles to becontrolled and allows particles having a high density and a controlledspecific surface area and being uniform in particle size to be obtained.

On the other hand, oxidation control is important also at the particlegrowth stage, and a concentration of oxygen in the space in the reactionvessel is preferably controlled in the same manner.

A concentration of oxygen in the atmosphere can be adjusted, forexample, using inert gas, such as nitrogen.

Examples of means to adjust a concentration of oxygen in the atmosphereto a predetermined concentration include continuous circulation of inertgas, such as nitrogen, through the atmosphere in the space inside thereaction vessel.

[Reaction Solution Temperature]

In the reaction vessel, a temperature of the reaction solution ispreferably set to not less than 20 degrees C., more preferably 20 to 60degrees C., further more preferably 35 to 60 degrees C.

When a temperature of the reaction solution is less than 20 degrees C.,solubility is low and therefore nuclei are easily formed and nucleiformation is hard to be controlled. Moreover, the primary particlesconstituting composite hydroxide particles are made finer, therebysometimes causing a too large specific surface area. On the other hand,a temperature of the reaction solution is more than 60 degrees C.,ammonia used for complex formation runs short due to volatilization ofammonia, and, as is the case with a temperature of less than 20 degreesC., solubility of metal ions easily decreases.

[Alkaline Solution]

The alkaline solution to adjust a pH value in the reaction solution isnot particularly limited, and, for example, an alkali metal hydroxidesolution, such as sodium hydroxide or potassium hydroxide, may be used.Said alkali metal hydroxide may be fed into the reaction solution as itis, but preferably added to the reaction solution in the reaction vesselin a form of solution because this makes it easier to control a pH valueof the reaction solution in the reaction vessel.

Moreover, a way of adding the alkaline solution to the reaction vesselis not particularly limited, and it is simply necessary that, with themixed solution sufficiently being stirred, the alkaline solution isadded by a pump capable of controlling a flow rate, such as a meteringpump, so as to maintain a pH value of the reaction solution in apredetermined range.

[Production Equipment]

In the above-mentioned composite hydroxide production step, there isused an apparatus having a system not to collect a product until areaction is completed. Examples of the apparatus include a batchreaction vessel which is commonly used and in which a stirrer isinstalled.

When such apparatus is adopted, unlike a common continuous crystallizerwhich collects a product by overflow, a problem that particles undergrowth are collected simultaneously together with an overflow liquiddoes not arise, and therefore particles having a narrow particle-sizedistribution and being uniform in particle diameter can be obtained.

Also, in order to control a reaction atmosphere, an apparatus capable ofcontrolling an atmosphere, such as a hermetically-sealed type apparatus,is preferably used.

The use of such apparatus allows the nucleation reaction and theparticle growth reaction to proceed almost uniformly, whereby particleshaving an excellent particle-size distribution (that is, particleshaving a narrow particle-size distribution range) can be obtained.

After completion of the particle growth stage, washing is performed toremove Na salts adhered to particles, whereby composite hydroxideparticles are obtained.

(B) Coating Step

In the coating step, the composite hydroxide particles obtained at theabove-mentioned particle production step are mixed with a solutioncontaining at least a tungsten compound and slurried, and the slurry iscontrolled to have a pH of 7 to 9 at a reference solution temperature of25 degrees C., whereby a coating material containing a metal oxide oftungsten and the additive element or a metal hydroxide of tungsten andthe additive element is formed on the surfaces of said compositehydroxide particles.

First, the above-mentioned composite hydroxide particles are slurred.The slurrying may be performed in such a manner that the compositehydroxide particles are mixed with a solution prepared in advance andcontaining a coating element, or after mixing of the composite hydroxideparticles with water, a compound containing a coating element is addedthereto.

A concentration of the composite hydroxide particles in theabove-mentioned slurry is preferably 100 to 300 g/L. A slurryconcentration of less than 100 g/L leads to too much liquid to betreated, whereby productivity is reduced, which is not preferable. Onthe other hand, a slurry concentration of more than 300 g/L sometimescauses the composite hydroxide particles not to be coated uniformly witha coating material. Almost the whole amount of tungsten ions andadditive element ions which are dissolved in the slurry are precipitatedas oxides or hydroxides on the surfaces of the composite hydroxideparticles.

Therefore, a tungsten compound and a compound containing the additiveelement to be added to the slurry are made to have a ratio of the numberof atoms shown in the above-mentioned general formula (1). Note that, inthe case where the additive element is added to the above-mentionedmixed solution, the additive element is added to the slurry in theamounts which are smaller by an amount of the additive element added tothe mixed solution, whereby a ratio of the number of atoms of metal ionsin the composite hydroxide particles to be obtained can be made inagreement with the ratio of the number of atoms shown in the generalformula (1).

After preparation of the slurry, the composite hydroxide particles andthe dissolved tungsten ions and the dissolved additive element ions arestirred so as to be uniformly mixed, and then acid, such as sulfuricacid, is added so that a pH value is adjusted to 7 to 9, preferably 8 to9 at a reference solution temperature of 25 degrees C.

Although a pH range of not more than 7 allows precipitation of tungsten,a too low pH value causes a problem that hydroxide dissolves, and also,an amount of sulfuric acid used is increased, thereby causing anincrease in cost. On the other hand, a pH value of more than 9 causesinsufficient precipitation of a tungsten oxide hydrate on the surfacesof the composite hydroxide particles.

In order to further improve thermal stability of a positive electrodeactive material, aluminum is preferably used to be added as an additiveelement. Addition of an aluminum compound into the slurry to performcrystallization of tungsten and aluminum simultaneously allows theabove-mentioned coating material to made into a mixture containing atungsten oxide hydrate and an aluminum hydroxide.

The tungsten compound to be used is not particularly limited as long asbeing stable in a form of a solution, but ammonium tungstate and/orsodium tungstate, which can be easily industrially handled, arepreferably used.

Ammonium tungstate has a low solubility in water, that is, approximately30 g/L, but, once dissolved, it is not precipitated even if a pH islowered to approximately 1. Also, even if ammonia is added in order tolower the solubility, the precipitation is difficult in an alkalinearea. However, when sulfuric acid is added in the presence of ammonia,adjustment of a pH value to 7 to 9 induces the precipitation, andfurthermore, the coexistence of the composite hydroxide particles toserve as nuclei allows precipitation on surfaces of the compositehydroxide particles, uniform crystallization of the coating material,and formation of a coating layer.

In the case of using ammonium tungstate, ammonia contained in a 25%ammonia solution in an amount equivalent to 0.5 to 25% by volume of anammonium tungstate saturated solution is preferably added to the slurry.If an amount of ammonia added is small, the tungsten oxide hydrate isdecomposed by sulfuric acid, whereby the precipitation thereof isprevented. On the other hand, if an amount of ammonia added is toolarge, sulfuric acid is only wasted for pH value adjustment, which isuneconomical. Preferably, ammonia contained in a 25% ammonia solution inan amount equivalent to 1 to 10% by volume of an ammonium tungstatesaturated solution is added, and then a pH value is adjusted to 7 to 9,whereby a composite hydroxide efficiently coated with a tungsten oxidehydrate on the surfaces of the composite hydroxide particles isobtained.

On the other hand, since sodium tungstate has a high solubility inwater, that is, approximately not less than 100 g/L, sodium tungstate isnot precipitated by simple pH adjustment, but the presence of thecomposite hydroxide particles which can serve as nuclei even without noaddition of ammonia allows sodium tungstate to be precipitated on thesurfaces of the particles and to made to more uniformly coat thesurfaces in the coexistence of aluminum.

An aluminum compound to be used is not particularly limited, but thereis preferably used sodium aluminate, which makes it possible toprecipitate aluminum hydroxide by adjusting a pH value with addition ofsulfuric acid. Thus, pH is controlled by addition of sulfuric acid tothe slurry so that tungsten and aluminum are simultaneously precipitatedas compounds, whereby the surfaces of the composite hydroxide particlescan be uniformly coated with a mixture containing tungsten oxide hydrateand aluminum hydroxide.

This coating step makes it possible to form a very fine and uniformcoating material on the surfaces of the composite hydroxide particles,and therefore an increase in specific surface area of the compositehydroxide can be controlled. Also, this coating step allows almost thewhole amount of tungsten in the slurry to be precipitated on thesurfaces of the composite hydroxide particles, and accordingly an amountof tungsten contained in the composite hydroxide is stabilized, andvariation in amount of tungsten between particles can be alsocontrolled.

2-1. Positive Electrode Active Material for Nonaqueous ElectrolyteSecondary Batteries

A positive electrode active material for nonaqueous electrolytesecondary batteries according to the present invention (hereinafterreferred to as a positive electrode active material according to thepresent invention) is suitable as a material for positive electrodes ofnonaqueous electrolyte secondary batteries.

The positive electrode active material according to the presentinvention is a positive electrode active material including a lithiumtransition metal composite oxide represented by the following generalformula (2) and having a layered hexagonal crystal structure, whereinthe positive electrode active material has an average particle diameterof 3 to 8 μm and an index indicating a scale of particle-sizedistribution, [(d₉₀−d₁₀)/average-particle-diameter], of not more than0.60.[Chemical Formula 4]Li_(1+u)M_(x)W_(s)A_(t)O₂  (2)

wherein,

−0.05≤u≤0.50, x+s+t=1, 0<s≤0.05, 0<s+t≤0.15,

M is at least one transition metal selected from Ni, Co and Mn, and

A is at least one additive element selected from transition metalelements other than M and W, group 2 elements, and group 13 elements.

[Particle Size Distribution]

The positive electrode active material according to the presentinvention has an index indicating a scale of particle-size distribution,[(d90−d10)/average-particle-diameter], of not more than 0.6.

When a particle size distribution is wide-ranging, many fine particleswhose particle diameter is considerably small with respect to an averageparticle diameter and many particles (coarse particles) whose particlediameter is considerably large with respect to the average particlediameter are present in the positive electrode active material.

In the case where a positive electrode is formed using the positiveelectrode active material including the many fine particles, a localreaction of the fine particles may cause heat generation, andaccordingly safety is lowered and also the fine particles areselectively degraded, whereby cycle characteristics are worsened. On theother hand, in the case where a positive electrode is formed using thepositive electrode active material including the many coarse particles,a reaction area of an electrolyte solution with the positive electrodeactive material cannot be sufficiently secured, and accordingly anincrease in reaction resistance causes a decrease in battery output.

Therefore, when the positive electrode active material is made to have aparticle-size distribution index, [(d90−d10)/average-particle-diameter],of not more than 0.6, a proportion of fine particles and coarseparticles is smaller and therefore a battery using this positiveelectrode active material for a positive electrode is excellent insafety and has good cycle characteristics and high battery-output.

Note that an average particle diameter (d50), and d10 and d90 eachrepresent the same as those represented in the case of theabove-mentioned transition metal composite hydroxide, and can becalculated in the same manner.

[Average Particle Diameter]

The positive electrode active material according to the presentinvention has an average particle diameter of 3 to 8 μm. In the casewhere an average particle diameter is less than 3 μm, the fillingdensity of particles is lowered when a positive electrode is formed,whereby a battery capacity per volume of the positive electrode isreduced. On the other hand, in the case where an average particlediameter is more than 8 μm, a specific surface area of the positiveelectrode active material is decreased to reduce an interface with anelectrolyte solution of a battery, whereby resistance of a positiveelectrode is increased to reduce output characteristics of the battery.

Therefore, when the positive electrode active material according to thepresent invention is adjusted to have an average particle diameter of 3to 8 μm, preferably 3 to 6 μm, a battery using this positive electrodeactive material for a positive electrode can have a largerbattery-capacity per volume and also have excellent batterycharacteristics, such as high safety and high output.

[Specific Surface Area]

The positive electrode active material according to the presentinvention preferably has a specific surface area of 0.5 to 2.0 m2/g.When a specific surface area is less than 0.5 m2/g, the positiveelectrode active material has a smaller contact area with an electrolytesolution, thereby causing a reaction surface area to be smaller and apositive electrode resistance to be increased, whereby outputcharacteristics of a battery are sometimes lowered. On the other hand,when a specific surface area is more than 2.0 m²/g, the positiveelectrode active material excessively contacts with an electrolytesolution, whereby thermal stability is sometimes lowered. In the presentinvention, the composite hydroxide having a controlled specific surfacearea is used as a precursor, and therefore a specific surface area ofthe positive electrode active material is also stably controlled in theabove-mentioned range.

[Composition of Particles]

The positive electrode active material according to the presentinvention has a composition represented by the above-mentioned generalformula (2), wherein a range of u, which represents an excessive amountof lithium, is −0.05≤u≤0.50. When the excessive amount of lithium, u, isless than −0.05, a positive electrode in a nonaqueous electrolytesecondary battery using the obtained positive electrode active materialhas a higher reaction resistance, and therefore battery output isreduced. On the other hand, when the excessive amount of lithium, u, ismore than 0.50, an initial discharge capacity in the case of using theabove-mentioned positive electrode active material for a positiveelectrode of a battery is decreased and also a reaction resistance ofthe positive electrode is increased.

Also, as represented by the general formula (2), in the positiveelectrode active material according to the present invention, tungstenis contained in a lithium transition metal composite oxide.

By making tungsten contained therein, positive electrode resistance canbe reduced and output characteristics of a battery using the lithiumtransition metal composite oxide as a positive electrode active materialcan be improved. When an amount of tungsten added exceeds an amount at aratio of tungsten with respect to all the metal elements other thanlithium of 0.05, battery capacity falls.

The additive element used for a positive electrode active material inorder to improve durable characteristics and output characteristics of abattery is preferably at least one element selected from B, Al, Sc, Y,Ti, Zr, Hf, V, Nb, Ta, Cr, and Mo, more preferably at least Al. Additionof Al allows thermal stability of the positive electrode active materialto be improved.

When an atomic ratio, s+t, of tungsten and an additive element A withrespect to all the metal elements other than lithium exceeds 0.15, metalelements contributing to a redox reaction are decreased, whereby batterycapacity falls. On the other hand, when s+t is not more than 0.02,improvement effects for output characteristics and thermal stability ofa battery are sometimes insufficient.

Therefore, the above-mentioned atomic ratio is preferably 0.02<s+t≤0.15.

Particularly, when tungsten and the additive element are uniformlydistributed on the surfaces or the inside of the particles, theabove-mentioned effects can be achieved in the whole particles, wherebyonly a small amount of addition thereof allows said effects to beobtained and an decrease in battery capacity to be controlled.

The positive electrode active material according to the presentinvention is preferably such that M in the above-mentioned generalformula (2) contains at least Ni and Co, specifically, the positiveelectrode active material is preferably a composite oxide represented bythe following general formula (2-1).[Chemical Formula 5]Li_(1+u)Ni_(1-x-s-t)Co_(x)W_(s)A_(t)O₂  (2-1)wherein,

−0.05≤u≤0.15, 0≤x≤0.2, 0<s≤0.05, 0<t≤0.15, x+s+t<0.3, and

A is at least one additive element selected from transition metalelements other than Ni, Co, and W, group 2 elements, and group 13elements.

The composition in the above-mentioned general formula (2-1) aims atachieving a battery having higher-capacity, and an amount of excessivelithium, u, is preferably −0.05≤u≤0.15 so that a battery can have bothhigh capacity and high output. Also, from viewpoints of battery capacityand thermal stability, a range of x representing the above-mentionedatomic ratio of Co is preferably 0≤x≤0.2.

Moreover, as another aspect, M preferably contains at least Ni and Mn,specifically, is preferably a composite oxide represented by thefollowing general formula (2-2).[Chemical Formula 6]Li_(1+u)Ni_(x)Mn_(y)Co_(z)W_(s)A_(t)O₂  (2-2)

wherein,

−0.05≤u≤0.50, x+y+z+s+t=1, 0.3≤x≤0.7, 0.1≤y≤0.55, 0≤z≤0.4, 0<s≤0.05,0<t≤0.15, and

A is at least one additive element selected from transition metalelements other than Ni, Co, Mn, and W, group 2 elements, and group 13elements.

In the case of the composition in the above-mentioned general formula(2-2), an amount of excessive lithium u is preferably −0.05≤u≤0.15 inorder to further reduce reaction resistance.

A range of x representing an atomic ratio of Ni is preferably 0.3≤x≤0.7.

Also, a range of y representing an atomic ratio of Mn is preferably0.1≤y≤0.55 so that a battery can have both high capacity and highoutput.

From viewpoints of battery capacity and thermal stability, a range of zrepresenting an atomic ratio of Co is preferably 0≤z≤0.4.

2-2. Method for Producing Positive Electrode Active Material forNonaqueous Electrolyte Secondary Batteries

A method for producing the positive electrode active material accordingto the present invention is not particularly limited as long as thepositive electrode active material can be produced so as to have theabove-mentioned average particle diameter, the particle sizedistribution, the specific surface area, and the composition, but thefollowing method is preferably applied because the above-mentionedpositive electrode active material can be more surely produced.

The method for producing the positive electrode active materialaccording to the present invention comprises the following three steps,as shown in FIG. 3.

(a) Heat treatment step of heat-treating a transition metal compositehydroxide which serves as a raw material of the positive electrodeactive material according to the present invention.

(b) Mixing step of mixing a lithium compound with the compositehydroxide after the heat treatment to form a lithium mixture.

(c) burning step of burning the lithium mixture formed in the mixingstep.

Hereinafter, each of the steps will be explained.

(a) Heat Treatment Step

The heat treatment step is a step wherein a transition metal compositehydroxide (hereinafter simply referred to as a composite hydroxide) isheat-treated to remove moisture contained in the composite hydroxide,and a temperature of the heat treatment is preferably 500 to 750 degreesC.

Particularly, the heat treatment of heating the composite hydroxide tothe above-mentioned temperature allows moisture to be removed and alsothe composite hydroxide to be converted into a transition metalcomposite oxide (hereinafter, simply referred to as a composite oxide),and therefore ratios of the number of atoms of metals and of the numberof atoms of lithium in the positive electrode active material obtainedcan be prevented from varying. Note that, with performing a treatment,such as implementation of an accurate analysis before the burning stepor implementation of analysis and correction after the mixing, the heattreatment step may be skipped, or with mainly aiming at removal ofcontained moisture, heat-treatment may be performed at a temperature ofnot less than 105 degrees C. and less than 500 degrees C.

In the case of a heating temperature of less than 500 degrees C. in theheat treatment step, a composite hydroxide is sometimes insufficientlyconverted into a composite oxide, on the other hand, in the case of aheating temperature of more than 750 degrees C., particles are sintered,whereby a composite oxide having a uniform particle diameter is notsometimes obtained.

An atmosphere for the heat treatment is not particularly limited and anon-reducing atmosphere is good enough, but the heat treatment ispreferably performed in air flow because the treatment can be easilyperformed.

Furthermore, a heat treatment time is not particularly limited, but aheat treatment time of less than 1 hour sometimes causes insufficientconversion of a composite hydroxide into compound oxide particles, andtherefore a heat treatment time is preferably at least 1 hour or more,more preferably 5 to 15 hours.

Also, equipment to be used for this heat treatment is not particularlylimited, and equipment capable of heating the composite hydroxide in anon-reducing atmosphere, preferably in air flow, is good enough, and anelectric furnace without generation of gas may be suitably used.

(b) Mixing Step

The mixing step is a step of mixing the composite hydroxide obtainedafter the above-mentioned heat treatment with a material containinglithium, for example, a lithium compound, thereby obtaining a lithiummixture. The composite hydroxide obtained after the heat treatment inthe mixing step includes a composite hydroxide obtained with skippingthe heat treatment step, a composite hydroxide obtained after removal ofresidual water in the heat treatment step, and a composite oxideobtained by the conversion in the heat treatment step.

The composite hydroxide obtained after the heat treatment and a materialcontaining lithium are mixed so that a ratio (Li/Me) of the number oflithium atoms (Li) to the total number of atoms of all the metalelements other than lithium (that is, the total number of atoms of M, W,and an additive element, (Me)) in the lithium mixture is 1:0.95 to1:1.50.

In other words, Li/Me hardly changes between before and after theburning step and Li/Me in the mixing step is to be Li/Me in the positiveelectrode active material, and therefore the mixing is performed so thatLi/Me in the lithium mixture is to be the same as Li/Me in the positiveelectrode active material to be obtained.

The material containing lithium used for forming the lithium mixture isnot particularly limited and a lithium compound is good enough. Forexample, lithium hydroxide, lithium nitrate, and lithium carbonate, anda mixture thereof are preferable because of the easy availability.

Note that the lithium mixture is preferably sufficiently mixed beforethe burning. When the mixing is insufficient, individual particles havedifferent Li/Me, whereby a problem that sufficient batterycharacteristics are not achieved or the like may arise.

In the mixing, an ordinary mixer, such as a shaker mixer, a Lodigemixer, a Julia mixer, or a V blender, may be used, and the compositeoxide particles are sufficiently mixed with the material containinglithium so that forms of the composite oxide particles and the like arenot broken.

(c) Burning Step

The burning step is a step of burning the lithium mixture obtained bythe above-mentioned mixing step to form a lithium transition metalcomposite oxide. When the lithium mixture is burned in the burning step,lithium in the material containing lithium is diffused into the compoundoxide particles, whereby a lithium transition metal composite oxide isformed.

[Burning Temperature]

The lithium mixture is burned at a temperature of 700 to 1000 degrees C.

When a burning temperature is less than 700 degrees C., lithium is notsufficiently diffused into the compound oxide particles, wherebyexcessive lithium and unreacted particles remain and a crystal structureis not sufficiently well-balanced, and consequently a problem thatsufficient battery characteristics are not obtained arises.

Also, when a burning temperature is more than 1000 degrees C., intensesintering between the compound oxide particles and also abnormalparticle growth may be caused, whereby there is a possibility thatparticles after burning become coarse and the particle form (the form ofsphere-shaped secondary particles mentioned at [0103] to [0108]) cannotbe maintained.

Such positive electrode active material has a smaller specific surfacearea and therefore when the positive electrode active material is usedfor a battery, a problem that positive electrode resistance is increasedand battery capacity is reduced arises.

Therefore, when the above-mentioned atomic ratio of Ni is not less than0.7, the lithium mixture is preferably burned at 700 to 800 degrees C.Also, when the above-mentioned atomic ratio of Mn is not less than 0.3,the lithium mixture is preferably burned at 800 to 1000 degrees C.

[Burning Time]

A burning time is preferably not less than 3 hours, more preferably 6 to24 hours. A burning time of less than 3 hours sometimes causesinsufficient formation of a lithium transition metal composite oxide.

[Calcination]

Particularly, in the case where lithium hydroxide, lithium carbonate, orthe like is used as a material containing lithium, calcination ispreferably performed before the burning with a temperature lower thanthe burning temperature and of 350 to 800 degrees C. for approximately 1to 10 hours.

In other words, calcination is preferably performed at a temperature ofreacting lithium hydroxide or lithium carbonate to the compositehydroxide obtained after the heat treatment. When a temperature ismaintained around the above-mentioned reaction temperature of lithiumhydroxide or lithium carbonate, lithium is sufficiently diffused intothe composite hydroxide obtained after the heat treatment, whereby auniform lithium transition metal composite oxide can be obtained.

[Burning Atmosphere]

The atmosphere for the burning is preferably an oxidizing atmosphere,more preferably an atmosphere having an oxygen concentration of 18 to100% by volume, still more preferably a mixed atmosphere of oxygen andinert gas.

In other words, the burning is preferably performed in the air or anoxygen current. There is a possibility that an oxygen concentration ofless than 18% by volume causes insufficient crystallinity of the lithiumtransition metal composite hydroxide. Particularly, in consideration ofbattery characteristics, it is preferable to perform the burning in anoxygen current.

Note that a furnace used for the burning is not particularly limited anda furnace capable of heating the lithium mixture in the air or an oxygencurrent is good enough, but an electric furnace without gas generationis preferably used, and any of a batch type furnace and a continuoustype furnace may be used.

[Pulverizing]

Aggregation or slight sintering of the lithium transition metalcomposite oxide obtained by the burning is sometimes caused, and in thiscase, the lithium transition metal composite oxide may be pulverized,whereby the positive electrode active material according to the presentinvention can be obtained.

Note that pulverizing means an operation being such that mechanicalenergy is supplied to an aggregation resulting from sintering necking orthe like between secondary particles at the time of the burning andcomposed of a plurality of secondary particles, whereby the secondaryparticles are separated almost without destroying the secondaryparticles and the aggregation is loosened.

3. Nonaqueous Electrolyte Secondary Battery

A nonaqueous electrolyte secondary battery according to the presentinvention is a battery adopting a positive electrode using the positiveelectrode active material for nonaqueous electrolyte secondary batteriesin accordance with a production flow chart illustrated in FIG. 4, thepositive electrode active material comprising a lithium transition metalcomposite oxide which uses a transition metal composite hydroxideaccording to the present invention as a precursor.

First, a structure of the nonaqueous electrolyte secondary batteryaccording to the present invention will be explained.

The nonaqueous electrolyte secondary battery according to the presentinvention (hereinafter sometimes simply referred to as a secondarybattery according to the present invention) has a structuresubstantially equivalent to an ordinary nonaqueous electrolyte secondarybattery, except that the positive electrode active material according tothe present invention is used as a material of a positive electrode.

Specifically, the secondary battery according to the present inventionhas a structure comprising a case, and a positive electrode, a negativeelectrode, a nonaqueous electrolyte solution, and a separator, eachbeing enclosed in said case.

More specifically, the secondary battery according to the presentinvention is formed in such a manner that the positive electrode and thenegative electrode are laminated via the separator to form an electrodebody; the obtained electrode body is impregnated with the nonaqueouselectrolyte solution; connection between a positive electrode currentcollector and a positive electrode terminal connected with an exteriorand connection between a negative electrode current collector and anegative electrode terminal connected with an exterior each areestablished using such as a lead for current collecting; and sealing inthe case is performed. As a shape of the secondary battery according tothe present invention, various shapes, such as a cylinder type and alaminated type, may be applied.

Note that a structure of the secondary battery according to the presentinvention is, needless to say, not limited to the above-mentionedexample, and can be realized in a form in which various changes andimprovements are made based on the knowledge of a person skilled in theart. Furthermore, use of the nonaqueous electrolyte secondary batteryaccording to the present invention is not particularly limited.

Hereinafter, each part constituting the secondary battery according tothe present invention will be explained.

(1) Positive Electrode

First, the positive electrode characterizing the secondary batteryaccording to the present invention will be explained.

A positive electrode is a sheet-like member and formed by, for example,applying a positive electrode mixture paste containing the positiveelectrode active material according to the present invention to asurface of the collector made of aluminum foil and then drying it.

Note that the positive electrode is processed to be suitable for abattery to be used. For example, a cutting treatment to cut the positiveelectrode into a size suitable for an objective battery, pressurizationand compression treatment by a roll press or the like in order toincrease electrode density, or the like is performed.

[Positive Electrode Mixture Paste]

The positive electrode mixture paste to be used is formed by adding asolvent to a positive electrode mixture and kneading it.

The positive electrode mixture is formed by mixing the positiveelectrode active material according to the present invention in powderform, an electric conductive material, and a binding agent.

The electric conductive material is added in order to provide suitableconductivity to the electrode. This electric conductive material is notparticularly limited, but examples of the electric conductive materialinclude graphite (natural graphite, artificial graphite, expandedgraphite, and the like) and a carbon black material, such as acetyleneblack and Ketchen black.

The binding agent plays a role which ties positive electrode activematerial particles.

The binding agent to be used for the positive electrode mixture is notparticularly limited, but examples of the binding agent includepolyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE),fluororubber, ethylene propylene diene rubber, styrene butadiene,cellulose resin, and polyacrylic acid.

Note that activated carbon or the like may be added to the positiveelectrode mixture. The addition of activated carbon or the like allowselectrical double-layer capacity to be increased.

The solvent plays a role in dissolving the binding agent to disperse thepositive electrode active material, the electric conductive material,the activated carbon, and the like into the binding agent. This solventis not particularly limited, but examples of the solvent include anorganic solvent, such as N-methyl-2-pyrrolidone.

A mixing ratio of each component in the positive electrode mixture pasteis not particularly limited. For example, when a solid content in thepositive electrode mixture except the solvent is taken as 100 parts bymass, as is the case with a positive electrode of an ordinary nonaqueouselectrolyte secondary battery, a content of the positive electrodeactive material may be 60 to 95 parts by mass, a content of the electricconductive material may be 1 to 20 parts by mass, and a content of thebinding agent may be 1 to 20 parts by mass.

(2) Negative Electrode

The negative electrode is a sheet-like member formed by applying anegative electrode mixture paste to a surface of a metallic foil currentcollector, such as copper, and then drying it. This negative electrodeis different from the above-mentioned positive electrode in componentconstituting the negative electrode mixture paste, formulation, currentcollector material, and the like, but is formed in substantially thesame manner as the positive electrode, and as is the case with thepositive electrode, each of the treatments is performed as needed.

The negative electrode mixture paste is formed in such a manner that anegative electrode active material is mixed with a binding agent to forma negative electrode mixture and an appropriate solvent is addedthereto, thereby making the negative electrode mixture into a pasteform.

As the negative electrode active material, there may be adopted, forexample, a material containing lithium, such as metallic lithium or alithium alloy, or a inclusion material capable of inclusion anddesorption of lithium ions.

The inclusion material is not particularly limited, but examples of theinclusion material include an organic compound burned material, such asnatural graphite, artificial graphite, and phenol resin, and powder of acarbon substance, such as coke.

In the case where said inclusion material is adopted as a negativeelectrode active material, as is the case with the positive electrode, afluorine-containing resin, such as PVDF, is usable as the binding agent,and as the solvent to disperse the negative electrode active materialinto the binding agent, an organic solvent, such asN-methyl-2-pyrrolidone, is usable.

(3) Separator

A separator is arranged so as to be sandwiched between the positiveelectrode and the negative electrode, and has a function to separate thepositive electrode and the negative electrode and maintain anelectrolyte. As said separator, for example, a thin film made ofpolyethylene, polypropylene, or the like and having many minute poresmay be used, but a material is not particularly limited as long as ithas the above-mentioned function.

(4) Nonaqueous Electrolyte Solution

A nonaqueous electrolyte solution is obtained by dissolving lithium saltas a supporting electrolyte in an organic solvent.

As the organic solvent, there may be used one kind alone or two or morekinds mixed, selected from the group consisting of a cyclic carbonate,such as ethylene carbonate, propylene carbonate, butylene carbonate, ortrifluoro propylene carbonate; a chain carbonate, such as diethylcarbonate, dimethyl carbonate, ethylmethyl carbonate, or dipropylcarbonate; an ether compound, such as tetrahydrofuran,2-methyltetrahydrofuran, or dimethoxyethane; a sulfur compound, such asethylmethylsulfone or butanesultone; a phosphorus compound, such astriethyl phosphate or trioctyl phosphate; and the like.

As the supporting electrolyte, LiPF6, LiBF4, LiClO4, LiAsF6,LiN(CF3SO2)2, a compound salt thereof, or the like may be used.

Note that, in order to improve battery characteristics, the nonaqueouselectrolyte solution may contain a radical scavenger, a surface activeagent, a flame retardant, and the like.

(5) Characteristics of Nonaqueous Electrolyte Secondary Battery

The nonaqueous electrolyte secondary battery according to the presentinvention is configured as mentioned above and uses the positiveelectrode active material according to the present invention, andtherefore, for example, in the case where the nonaqueous electrolytesecondary battery is a 2032 type coin battery, a high initial dischargecapacity of not less than 150 mAh/g and a low positive electroderesistance of not more than 5Ω can be achieved and thus the battery hashigh capacity and high output. Furthermore, compared with a batteryusing a prior positive electrode active material composed of lithiumcobalt oxide or lithium nickel oxide, the nonaqueous electrolytesecondary battery according to the present invention has higher thermalstability and is more excellent in safety.

(6) Use of Nonaqueous Electrolyte Secondary Battery

The nonaqueous electrolyte secondary battery according to the presentinvention has the above-mentioned characteristics, and therefore issuitable for power sources of small portable electronic equipment (suchas notebook-sized personal computers and cell phones) in which highcapacity is always required.

Furthermore, the nonaqueous electrolyte secondary battery according tothe present invention is suitable also for power sources for drivingmotors in which high output is required. A larger size battery causesdifficulty in securing safety, thereby absolutely requiring an expensiveprotection circuit, but the nonaqueous electrolyte secondary batteryaccording to the present invention has excellent safety, and thereforenot only safety is more easily secured but also an expensive protectioncircuit is simplified, thereby leading to low cost. Furthermore, sinceminiaturization and high output can be achieved, the nonaqueouselectrolyte secondary battery according to the present invention issuitable as a power source for transport equipment which is underrestrictions on loading space.

EXAMPLES

Hereinafter, Examples will explain the present invention in more detail.

In Examples, a composite hydroxide produced by the method according tothe present invention and a positive electrode active material producedby using said composite hydroxide as a precursor with the methodaccording to the present invention were examined to confirm therespective average particle diameters and the respective particle sizedistributions.

Also, for a secondary battery which has a positive electrode using thepositive electrode active material produced by the method according tothe present invention, its characteristics (initial discharge capacity,positive electrode resistance, and thermal stability) were examined.

The present invention is not limited at all by these Examples.

“Measurement of average particle diameter”, “measurement of particlesize distribution”, “identification and confirmation of crystalstructure”, “composition analysis”, and “production of secondary battery(including evaluation thereof)” in Examples were performed as follows.

[Measurement of Average Particle Diameter and Particle SizeDistribution]

An average particle diameter and a particle size distribution([(d₉₀−d₁₀)/average-particle-diameter] value) were calculated from anintegrated value of volume measured by a laser diffraction scatteringtype particle-size-distribution measurement apparatus (Microtrac HRA,manufactured by Nikkiso Co., Ltd.).

[Identification and Confirmation of Crystal Structure]

A crystal structure was identified and confirmed by X-ray diffractionmeasurement (“X'Pert PRO”, manufactured by PANalytical).

[Composition Analysis]

After a sample was dissolved, a composition was analyzed by ICP emissionspectrometry.

[Production of Secondary Battery]

For evaluation, a 2032 type coin battery shown in FIG. 5 (hereinafter,referred to as a coin type battery B) was produced and used.

As shown in FIG. 5, the coin type battery B is configured with a case(positive electrode can 5 and negative electrode can 6) and an electrode(positive electrode 1 and negative electrode 2) housed in the case.

The case comprises the positive electrode can 5 having a hollow and anopening portion at one end, and the negative electrode can 6 arranged inthe opening portion of the positive electrode can 5; and is configuredsuch that, when the negative electrode can 6 is arranged in the openingportion of the positive electrode can 5, a space to house the electrodebetween the negative electrode can 6 and the positive electrode can 5 isformed.

The electrode comprises the positive electrode 1 and the negativeelectrode 2, and a separator 3 is interposed between the positiveelectrode 1 and the negative electrode 2 so that they are laminated. Theelectrode is housed in the case so that the positive electrode 1 comesinto contact with an inner surface of the positive electrode can 5,while the negative electrode 2 comes into contact with an inner surfaceof the negative electrode can 6.

Note that the case is equipped with a gasket 4, and the gasket 4 allowsthe positive electrode can 5 and the negative electrode can 6 to befixed so as to keep an electrically insulating state between thepositive electrode can 5 and the negative electrode can 6. The gasket 4also has a function to seal a gap between the positive electrode can 5and the negative electrode can 6 to airtightly and fluidtightly separatean interior of the case from an exterior thereof.

The above-mentioned coin type battery B was produced as follows.

First, 52.5 mg of a positive electrode active material for nonaqueouselectrolyte secondary batteries, 15 mg of acetylene black, and 7.5 mg ofpolytetrafluoroethylene resin (PTFE) were mixed, and press-formed at apressure of 100 MPa to be 11 mm in diameter and 100 μm in thickness,whereby a positive electrode 1 was produced. Next, the obtained positiveelectrode 1 was dried in a vacuum dryer at 120 degrees C. for 12 hours.

Using this positive electrode 1, a negative electrode 2, a separator 3,and an electrolyte solution, a coin type battery B was produced in aglove box with an Ar atmosphere in which a dew point was controlled at−80 degrees C.

Note that, for the negative electrode 2, there was used a Li metalhaving a diameter of 17 mm and a thickness of 1 mm. For the separator 3,there was used a porous polyethylene film having a film thickness of 25μm.

For the electrolyte solution, there was used a mixture solution ofethylene carbonate (EC) and diethyl carbonate (DEC) in equalproportions, wherein 1 M of LiClO4 was used as a supporting electrolyte(manufactured by Tomiyama Pure Chemical Industries, Limited).

For evaluation of characteristics of the obtained coin type battery B,initial discharge capacity, positive electrode resistance, and thermalstability were defined as follows.

Initial discharge capacity was defined in such a manner that the cointype battery B was left to stand for 24 hours after producing thereof;after an open circuit voltage (OCV) was stabilized, with a currentdensity for a positive electrode being set to 0.1 mA/cm², charging wasperformed until a cut-off voltage reached 4.3 V; and then, after a1-hour suspension, discharging was performed until the cut-off voltagereached 3.5 V, and a capacity at the time of this discharging wasregarded as an initial discharge capacity.

Positive electrode resistance was evaluated in such a manner that thecoin type battery B was charged to have a charging electric potential of4.1 V, and, measurement was performed using a frequency responseanalyzer and a potentiogalvanostat (1255B, manufactured by Solartron)with an alternating-current-impedance method, whereby a Nyquist plotshown in FIG. 6 was produced.

This Nyquist plot is expressed as the sum of characteristic curvesrepresenting a solution resistance, a negative electrode resistance anda capacity thereof, and a positive electrode resistance and a capacitythereof, and therefore, based on this Nyquist plot, a fittingcalculation was performed using an equivalent circuit to calculate avalue of the positive electrode resistance.

Thermal stability was evaluated in such a manner that charging wasperformed until a charging electric potential reached 4.575 V, and thena coin cell was disassembled and a positive electrode was taken outthereof, and variation in amount of heat between from 80 to 400 degreesC. was measured with a Differential scanning calorimeter (DSC3100SA,manufactured by MAC Science), thereby being evaluated as a heatgeneration starting temperature.

Example 1

[Composite Hydroxide Particle Production Step]

First, while a reaction vessel (34 L) was filled half full with waterand stirred, a temperature in the vessel was set to 40 degrees C., andnitrogen gas was circulated through the reaction vessel to create anitrogen gas atmosphere.

An oxygen concentration in a space inside the reaction vessel at thistime was 2.0% by volume, and a concentration of oxygen dissolved in asolution in the reaction vessel was not more than 2 mg/L.

To the water in the reaction vessel, 25% by mass of a sodium hydroxidesolution and 25% by mass of aqueous ammonia were added in proper amountto adjust a pH to 12.6 at a reference solution temperature of 25 degreesC. Furthermore, an ammonium ion concentration in a reaction solution wasadjusted to 15 g/L.

<Nucleation Stage>

Next, nickel sulfate and cobalt sulfate were dissolved in water toobtain 1.8 mol/L of a mixed solution. This mixed solution was adjustedas to have a molar ratio of metal elements of Ni:Co of 0.82:0.15.

The above-mentioned mixed solution was added to the reaction solution inthe reaction vessel at a rate of 88 ml/min. At the same time, 25% bymass of aqueous ammonia and 25% by mass of a sodium hydroxide solutionwere also added to the reaction solution in the reaction vessel at aconstant flow rate, and, in a state where an ammonium ion concentrationin the obtained solution for nucleation was maintained at theabove-mentioned value, with a pH value being controlled to 12.6(nucleation pH) at a reference solution temperature of 25 degrees C.,crystallization was performed for 2 minutes and 30 seconds to carry outnucleation.

<Particle Growth Stage>

After that, only 25% by mass of the sodium hydroxide solutiontemporarily stopped being supplied until a pH value of the solution fornucleation reached 11.6 (particle growth pH), whereby a solution forparticle growth was obtained.

After a pH value of the obtained solution for particle growth reached11.6 at a reference solution temperature of 25 degrees C., supply of 25%by mass of the sodium hydroxide solution was resumed, and, with the pHvalue being maintained at 11.6, particle growth was performed for 2hours.

When the reaction vessel was filled to capacity, the supply of thesodium hydroxide solution was stopped, and stirring was also stopped,followed by still standing, whereby precipitation of a product wasfacilitated. Then, after a half amount of a supernatant liquid was takenout from the reaction vessel, the supply of the sodium hydroxidesolution was resumed and crystallization was performed for another 2hours (4 hours in total), and then the particle growth was terminated.Then, the obtained product was water-washed, filtered and dried, wherebycomposite hydroxide particles were collected.

[Coating Step]

In order that the obtained particles were coated with tungsten andaluminum and had a molar ratio of Ni:Co:Al:W of 82:15:3:0.5, 100 g ofhydroxide particles, water, sodium aluminate, and 37 ml of a 30 g/Lconcentration of an ammonium tungstate solution were put in a 500 mLbeaker and mixed to achieve a slurry concentration of 200 g/L at thetime of completion of coating. After 3.7 ml of 25% by mass of aqueousammonia, equivalent to 10% by volume of the ammonium tungstate solution,was added, 8% by mass of sulfuric acid was added so as to achieve afinal pH of 8.5 at a normal temperature (25 to 30 degrees C.), therebyperforming coating.

Then, a whole amount of a hydroxide slurry in the vessel was filteredand collected, and water-washed by pouring water, and then dried at 120degrees C. for not less than 12 hours, whereby a composite hydroxiderepresented by Ni0.82Co0.15Al0.03W0.005(OH)2+α (0≤α≤0.5) was obtained.

A specific surface area of the composite hydroxide was measured by BETmethod, and was 8.6 m2/g.

[Positive Electrode Active Material Production Step]

<Heat Treatment Step>

The above-mentioned composite hydroxide was heat-treated in an aircurrent (oxygen concentration: 21% by volume) at a temperature of 700degrees C. for 6 hours to obtain a composite oxide.

<Mixing Step>

Lithium hydroxide was weighed so as to achieve Li/Me of 1.02 (atomicratio) and mixed with the compound oxide particles obtained above,whereby a lithium mixture was obtained. The mixing was performed using ashaker mixer (TURBULA TypeT2C, manufactured by Willy A. Bachofen (WAB)).

<Burning Step>

The obtained mixture was calcinated in an oxygen current (oxygenconcentration: 100% by volume) at 500 degrees C. for 4 hours, and thenburned at 730 degrees C. for 24 hours, and after being cooled,pulverized, whereby a positive electrode active material was obtained.The positive electrode active material had a composition ofLi_(1.02)Ni_(0.816)Co_(0.149)Al_(0.030)W_(0.005)O₂. A specific surfacearea of the positive electrode active material was measured by BETmethod, and was 0.67 m²/g.

Table 1 shows average particle diameters,[(d₉₀−d₁₀)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 2

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 1, except that, in the composite hydroxide particle productionstep, a mixed solution was prepared so as to have a molar ratio of metalelements of Ni:Co:Ti of 82:15:1 and crystallized, and coating wasperformed so as to achieve a molar ratio of Ni:Co:Ti:Al:W of82:15:1:2:0.5.

The positive electrode active material had a composition ofLi_(1.02)Ni_(0.816)Co_(0.149)Ti_(0.010)Al_(0.020)W_(0.005)O₂.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 8.9 m²/gand 0.72 m²/g, respectively.

Table 1 shows average particle diameters,[(d₉₀−d₁₀)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 3

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 1, except that, in the composite hydroxide particle productionstep, a mixed solution was prepared so as to have a molar ratio of metalelements of Ni:Co:Zr of 82:15:0.5 and crystallized, and coating wasperformed so as to achieve a molar ratio of Ni:Co:Zr:Al:W of82:15:0.5:2:0.5.

The positive electrode active material had a composition ofLi_(1.02)Ni_(0.82)Co_(0.15)Al_(0.02)Zr_(0.005)W_(0.005)O₂.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 9.0 m²/gand 0.77 m²/g, respectively.

Table 1 shows average particle diameters,[(d₉₀−d₁₀)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 4

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 1, except that, in the composite hydroxide particle productionstep, a mixed solution was prepared so as to have a molar ratio of metalelements of Ni:Co:Mn of 8:1:1 and crystallized and coating was performedso as to achieve a molar ratio of Ni:Co:Mn:W of 80:10:10:0.5; and in thepositive electrode active material production step, the heat treatmenttemperature was set to 550 degrees C., the mixing was performed so as toachieve Li/Me of 1.10, and the burning temperature was set to 800degrees C.

The positive electrode active material had a composition ofLi1.10Ni0.796Co0.100Mn0.100W0.005O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 12.1m2/g and 1.05 m2/g, respectively.

Table 1 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 5

[Composite Hydroxide Particle Production Step]

While a small type reaction vessel (5 L) was filled half full with waterand stirred, a temperature in the vessel was set to 40 degrees C. Intothe reaction vessel, 25% by mass of a sodium hydroxide solution and 25%by mass of aqueous ammonia were added in proper amount thereby to adjusta pH to 12.6 at a reference solution temperature of 25 degrees C. andadjust an ammonium ion concentration in a reaction solution to 10 g/L.

<Nucleation Stage>

Next, 1.8 mol/L of a mixed solution obtained by dissolving nickelsulfate and cobalt sulfate (a molar ratio of metal elements of Ni:Co of82:15) in water, and 25% by mass of aqueous ammonia and 25% by mass of asodium hydroxide solution were added to the above-mentioned reactionsolution at a constant flow rate thereby to obtain a solution fornucleation, and in a state where an ammonium ion concentration in theobtained solution for nucleation was maintained at the above-mentionedvalue, with a pH value being controlled to 12.6 (nucleation pH) at areference solution temperature of 25 degrees C., a sodium hydroxidesolution was added for 2 minutes and 30 seconds thereby to obtain a seedcrystal.

<Particle Growth Stage>

While another reaction vessel (34 L) was filled half full with water andstirred, a temperature in the vessel was set to 40 degrees C., andnitrogen gas was circulated therethrough to create a nitrogen gasatmosphere. An oxygen concentration in a space inside the reactionvessel at this time was 2.0% by volume.

To the water in the reaction vessel, 25% by mass of a sodium hydroxidesolution and 25% by mass of aqueous ammonia were added in proper amountto adjust a pH to 11.6 at a reference solution temperature of 25 degreesC. Furthermore, an ammonium ion concentration in a reaction solution wasadjusted to 10 g/L. The reaction solution containing the seed crystalobtained in the small type reaction vessel was fed into the reactionvessel, and then, in a state where an ammonium ion concentration in thesolution for particle growth was maintained at the above-mentionedvalue, with the pH value being controlled to 11.6, the above-mentionedmixed solution, the aqueous ammonia, and the sodium hydroxide solutioncontinued to be added for 2 hours to perform particle growth.

When the reaction vessel was filled to capacity, the supply of theaqueous ammonia and the sodium hydroxide solution were stopped, andstirring was also stopped, followed by still standing, wherebyprecipitation of a product was facilitated. After the product wasprecipitated and then a half amount of supernatant liquid was taken outfrom the reaction vessel, the supply of the aqueous ammonia and thesodium hydroxide solution were resumed. The aqueous ammonia and thesodium hydroxide solution were supplied for another 2 hours (4 hours intotal), and then the supply of them was terminated, and the obtainedparticles were water-washed, filtered and dried, and then collected.

[Coating Step]

A composite hydroxide was obtained by coating in the same manner as inExample 1, except that the obtained particles were coated and had amolar ratio of Ni:Co:Al:W of 82:15:3:1.

The remainder steps were performed in the same manner as in Example 1,whereby a positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated.

The positive electrode active material had a composition ofLi1.02Ni0.812Co0.149Al0.030W0.010O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 9.0 m2/gand 0.82 m2/g, respectively.

Table 1 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Comparative Example 1

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 1, except that, in the coating step, an ammonia solution was notadded, and the coating is performed so as to achieve a molar ratio ofNi:Co:Al of 82:15:3.

The positive electrode active material had a composition ofLi1.02Ni0.82Co0.15Al0.03O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 8.6 m2/gand 0.70 m2/g, respectively.

Table 1 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

TABLE 1 Positive electrode active material Composite hydroxide (d₉₀-Initial DSC heat Average (d₉₀-d₁₀)/ Average d₁₀)/ discharge Positivegeneration particle average particle average capacity electrode startingdiameter particle diameter particle [mAh · resistance temperature [μm]diameter Li/Me s s + t [μm] diameter g⁻¹] [Ω] [° C.] Example 1 4.5 0.481.02 0.005 0.035 4.6 0.55 191.1 2.3 198 Example 2 4.1 0.49 1.02 0.0050.035 4.3 0.52 190.9 2.0 199 Example 3 3.9 0.50 1.02 0.005 0.030 4.40.55 190.3 2.2 197 Example 4 4.3 0.51 1.10 0.005 0.005 4.7 0.59 188.13.0 202 Example 5 4.1 0.47 1.10 0.010 0.040 4.3 0.58 191.2 2.3 199Comparative 4.5 0.48 1.02 0 0.030 4.5 0.56 191.0 3.9 197 Example 1

(Evaluation)

It is found that Examples 1 to 5, which have the respective averageparticle diameters and the respective average particle sizedistributions according to the present invention and to which tungstenwas added, have higher capacity and lower positive electrode resistanceand are suitable as positive electrode active materials for nonaqueouselectrolyte secondary batteries. On the other hand, it is found thatComparative Example 1, to which tungsten was not added, has highercapacity but has higher positive electrode resistance, and hence outputcharacteristics are not sufficient.

Example 6

[Hydroxide Particle Production Step]

First, while a reaction vessel was filled half full with water andstirred, a temperature in the vessel was set to 40 degrees C., andnitrogen gas was circulated through the reaction vessel to create anitrogen gas atmosphere. An oxygen concentration in a space inside thereaction vessel at this time was 3.0% by volume, and a concentration ofoxygen dissolved in a solution in the reaction vessel was not more than2 mg/L. To the solution in the reaction vessel, 25% by mass of a sodiumhydroxide solution and 25% by mass of aqueous ammonia were added inproper amount to adjust a pH to 12.6 at a reference solution temperatureof 25 degrees C., and an ammonia concentration in the solution wasadjusted to 10 g/L. To the obtained solution, 2.0 mol/L of a solutionobtained by dissolving nickel sulfate and manganese sulfate (a molarratio of metal elements of Ni:Mn of 50:50) in water, and 25% by mass ofaqueous ammonia and 25% by mass of a sodium hydroxide solution wereadded at a constant flow rate, and, with a pH value being controlled to12.6 (nucleation pH), crystallization was performed for 2 minutes and 30seconds.

After that, only the supply of 25% by mass of the sodium hydroxidesolution was temporarily stopped until a pH value reached 11.6 (nucleusgrowth pH) at a reference solution temperature of 25 degrees C., andafter the pH value reached 11.6 at a reference solution temperature of25 degrees C., the supply of 25% by mass of the sodium hydroxidesolution was resumed. With the pH value being maintained at 11.6 and thepH fluctuation range being controlled within plus and minus 0.2 of apredetermined value, crystallization was continued for 2 hours, and atthe time when the reaction vessel was filled to capacity, thecrystallization was stopped, and stirring was also stopped, followed bystill standing, whereby precipitation of a product was facilitated.Then, after a half amount of supernatant liquid was taken out from thereaction vessel, the crystallization was resumed.

The crystallization was performed for another 2 hours (4 hours intotal), and then the crystallization was terminated, and the product waswater-washed, filtered and dried. By the above-mentioned method,composite hydroxide particles represented by Ni0.50Mn0.50(OH)2+α(0≤α≤0.5) were obtained.

[Coating Step]

In order that the obtained particles were coated with tungsten and had amolar ratio of Ni:Mn:W of 49.75:49.75:0.5, 100 g of the hydroxideparticles, water, and 37 ml of a 30 g/L concentration of an ammoniumtungstate solution were put in a 500 mL beaker and mixed to achieve aslurry concentration of 200 g/L at the time of completion of coating.After 3.7 ml of 25% by mass of aqueous ammonia, equivalent to 10% byvolume of the ammonium tungstate solution, was added, 8% by mass ofsulfuric acid was added so as to achieve a final pH value of 8.5 at anormal temperature, thereby performing coating.

Then, a whole amount of hydroxide slurry in the vessel was filtered andcollected, and water-washed by pouring water, and then dried at 120degrees C. for not less than 12 hours, whereby a composite hydroxiderepresented by Ni0.498Mn0.498W0.005(OH)2+α (0≤α≤0.5) was obtained. Aspecific surface area of the composite hydroxide was measured by BETmethod, and was 20.2 m2/g.

[Positive Electrode Active Material Production Step]

<Heat Treatment Step>

The above-mentioned composite hydroxide was heat-treated in an aircurrent (oxygen concentration: 21% by volume) at a temperature of 700degrees C. for 6 hours to obtain a composite oxide.

<Mixing Step>

Lithium carbonate was weighed so as to achieve Li/Me of 1.35 andsufficiently mixed with the obtained compound oxide by a shaker mixer(TURBULA TypeT2C, manufactured by Willy A. Bachofen (WAB)) to obtain alithium mixture.

<Burning Step>

The obtained lithium mixture was calcinated in an air current (oxygenconcentration: 21% by volume) at 400 degrees C. for 4 hours, and thenburned at 980 degrees C. for 10 hours, and pulverized to obtain apositive electrode active material for nonaqueous electrolyte secondarybatteries.

The positive electrode active material had a composition ofLi1.35Ni0.498Mn0.498W0.005O2.

A specific surface area of the positive electrode active material wasmeasured by BET method, and was 1.4 m2/g.

Table 2 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries. FIG. 7 shows SEM (scanning electronmicroscope JSM-6360LA, manufactured by JEOL Ltd.) observation results ofthe positive electrode active material.

Example 7

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 6, except that, in the coating step, the mixing was performed soas to achieve a molar ratio of Ni:Mn:W of 47.5:47.5:5, and 37 ml of 25%by mass of aqueous ammonia, equivalent to 10% by volume of 370 ml of anammonium tungstate solution, was added.

The obtained composite hydroxide had a composition ofNi0.475Mn0.475W0.05(OH)2+α (0≤α≤0.5), and the positive electrode activematerial had a composition of Li1.35Ni0.475Mn0.475W0.05O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 21.9m2/g and 1.5 m2/g, respectively.

Table 2 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 8

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 6, except that, in the coating step, the mixing was performed soas to achieve a molar ratio of Ni:Mn:Al:W of 48.3:48.3:3:0.5.

The obtained composite hydroxide had a Ni0.483Mn0.483Al0.03W0.005(OH)2+α(0≤α≤0.5), and the positive electrode active material had a compositionof Li1.35Ni0.483Mn0.483Al0.03W0.05O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 26.3m2/g and 1.4 m2/g, respectively.

Table 2 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Comparative Example 2

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 6, except that the final pH value was controlled to 11.

Tungsten was not precipitated, the obtained composite hydroxide had acomposition of Ni0.50Mn0.50(OH)2+α (0≤α≤0.5), and the positive electrodeactive material had a composition of Li1.35Ni0.50Mn0.50O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 21.1m2/g and 1.3 m2/g, respectively.

Table 2 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Comparative Example 3

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 6, except that the final pH value was controlled to 5.

A part of hydroxide particles dissolved in the coating step, andaccordingly, subsequent processes were discontinued. A specific surfacearea of the composite hydroxide after the coating step was measured byBET method, and was 31.5 m²/g.

TABLE 2 Composite hydroxide Positive electrode active material (d₉₀-(d₉₀- Initial DSC heat Average d₁₀)/ Average d₁₀)/ discharge Positivegeneration particle average particle average capacity electrode startingdiameter particle diameter particle [mAh · resistance temperature [μm]diameter Li/Me s s + t [μm] diameter g⁻¹] [Ω] [° C.] Example 6 5.5 0.461.35 0.005 0.005 5.6 0.51 201.1 5.6 215 Example 7 5.5 0.46 1.35 0.0500.050 5.7 0.52 200.5 5.4 220 Example 8 5.5 0.46 1.35 0.005 0.035 5.60.51 195.7 5.9 233 Comparative 5.5 0.46 1.35 0 0 5.4 0.51 200.9 8.5 223Example 2

(Evaluation)

It is found that Examples 6 to 8, which have the respective averageparticle diameters and the respective particle size distributionsaccording to the present invention and to which tungsten was added, havehigher capacity and lower positive electrode resistance and are suitableas positive electrode active materials for nonaqueous electrolytesecondary batteries. On the other hand, it is found that ComparativeExample 2, to which tungsten was not added, has considerably higherpositive electrode resistance and hence has a problem as a positiveelectrode active material for nonaqueous electrolyte secondarybatteries.

Example 9

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 6, except that, in the composite hydroxide production step, amixed solution was prepared so as to have a molar ratio of metalelements of Ni:Co:Mn of 33:33:33 and crystallized; in the coating step,coating was performed so as to achieve a molar ratio of Ni:Co:Mn:W of33.1:33.1:33.1:0.5; and in the positive electrode active materialproduction step, the heat treatment was not performed, the mixing wasperformed so as to achieve Li/Me of 1.15, the calcination temperaturewas set to 760 degrees C., and the burning temperature was set to 900degrees C.

The obtained composite hydroxide had a composition ofNi_(0.331)Co_(0.331)Mn_(0.331)W_(0.005)(OH)_(2-α) (0≤α≤0.5) and thepositive electrode active material had a composition ofLi_(1.15)Ni_(0.331)Co_(0.331)Mn_(0.331)W_(0.005)O₂.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 19.1m2/g and 1.0 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 10

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 9, except that, in the coating step, the mixing was performed soas to achieve a molar ratio of Ni:Co:Mn:W of 31.7:31.7:31.7:5, and 3.7ml of 25% by mass of aqueous ammonia, equivalent to 1% by volume of 370ml of an ammonium tungstate solution, was added.

A small amount of tungsten remained in the slurry, and consequently theobtained composite hydroxide had a composition ofNi0.321Co0.321Mn0.321W0.036(OH)2+α (0≤α≤0.5), and the positive electrodeactive material had a composition ofLi1.15Ni0.321Co0.321Mn0.321W0.036O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 19.3m2/g and 1.1 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 11

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 9, except that, in the coating step, the mixing was performed soas to achieve a molar ratio of Ni:Co:Mn:Al:W of 32.2:32.2:32.2:3:0.5.

The obtained composite hydroxide had a composition ofNi0.322Co0.322Mn0.322Al0.03W0.005(OH)2+α (0≤α≤0.5), and the positiveelectrode active material had a composition ofLi1.15Ni0.322Co0.321Mn0.322Al0.03W0.005O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 18.2m2/g and 0.97 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Example 12

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 11, except that, in the coating step, the mixing was performedusing sodium tungstate instead of ammonium tungstate so as to achieve amolar ratio of Ni:Co:Mn:Al:W of 32.2:32.2:32.2:3:0.5, and ammonia wasnot added.

The obtained composite hydroxide had a composition ofNi0.322Co0.322Mn0.322Al0.03W0.005(OH)2+α (0≤α≤0.5), and the positiveelectrode active material had a composition ofLi1.15Ni0.322Co0.322Mn0.322Al0.03W0.005O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 19.5m2/g and 1.1 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Comparative Example 4

To a 5-liter cylinder-type reaction vessel (a modified cylindricalcontainer made of stainless steel) equipped with a stirrer and aoverflow pipe, pure water and 25% by mass of a sodium hydroxide solution(an extra-pure reagent, manufactured by Wako Pure Chemical Industries,Ltd.) were added so as to achieve a pH of 11.3, and, with a temperaturebeing maintained at 35 degrees C., stirring was performed at a constantflow rate. Next, a mixed solution was added at a flow rate of 4 ml/min,the mixed solution being obtained by mixing a nickel sulfate solution(an extra-pure reagent, manufactured by Wako Pure Chemical Industries,Ltd.), a cobalt sulfate solution (an extra-pure reagent, manufactured byWako Pure Chemical Industries, Ltd.), and a manganese sulfate solution(an extra-pure reagent, manufactured by Wako Pure Chemical Industries,Ltd.) so as to achieve an atomic ratio of Ni:Co:Mn of 1:1:1 and have atotal salt concentration of 2 mol/L. At the same time, 25% by mass ofaqueous ammonia (an extra-pure reagent, manufactured by Wako PureChemical Industries, Ltd.) was added to the reaction vessel as acomplexing agent at a flow rate of 0.4 ml/min. Furthermore, 25% by massof a sodium hydroxide solution was intermittently added so as to controla pH value of a reaction solution to 11.5 to 12.0 at a referencesolution temperature of 25 degrees C., whereby nickel-cobalt-manganesecomposite hydroxide particles were formed.

After the state inside the reaction vessel became stationary, thenickel-cobalt-manganese composite hydroxide particles were continuouslycollected from the overflow pipe, water-washed, and filtered, and thenair-dried at 120 degrees C. for 24 hours, whereby nickel cobaltmanganese composite hydroxide particles were obtained. A pH of apost-reaction solution was measured and as a result, was 11.85 at areference solution temperature of 25 degrees C.

In subsequent processes, the same manner as in Example 9 was applied toobtain and evaluate a positive electrode active material for nonaqueouselectrolyte secondary batteries.

The obtained composite hydroxide had a composition ofNi0.332Co0.332Mn0.332W0.005(OH)2+α (0≤α≤0.5), and the positive electrodeactive material had a composition ofLi1.15Ni0.332Co0.332Mn0.332W0.005O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 31.8m2/g and 2.1 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Comparative Example 5

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 9, except that the coating step was not performed andaccordingly the composite hydroxide particles were not coated withtungsten.

The obtained composite hydroxide had a composition ofNi0.333Co0.333Mn0.333(OH)2+α (0≤α≤0.5), and the positive electrodeactive material had a composition of Li1.15Ni0.333Co0.333Mn0.333O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 19.7m2/g and 1.5 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

Comparative Example 6

A positive electrode active material for nonaqueous electrolytesecondary batteries was obtained and evaluated in the same manner as inExample 9, except that, in the coating step, the mixing was performed soas to achieve a molar ratio of Ni:Co:Mn:Al of 32.3:32.3:32.3:3, andaqueous ammonia was not added.

The obtained composite hydroxide had a composition ofNi0.323Co0.323Mn0.323Al0.03(OH)2+α (0≤α≤0.5), and the positive electrodeactive material had a composition of Li1.15Ni0.32Co0.32Mn0.32Al0.03O2.

Specific surface areas of the composite hydroxide and the positiveelectrode active material were measured by BET method, and were 20.5m2/g and 1.6 m2/g, respectively.

Table 3 shows average particle diameters,[(d90−d10)/average-particle-diameter] values, positive electroderesistance, and thermal stability of the obtained composite hydroxideand the obtained positive electrode active material for nonaqueouselectrolyte secondary batteries.

TABLE 3 Composite hydroxide Positive electrode active material (d₉₀-(d₉₀- Initial DSC heat Average d₁₀)/ Average d₁₀)/ discharge Positivegeneration particle average particle average capacity electrode startingdiameter particle diameter particle [mAh · resistance temperature [μm]diameter Li/Me s s + t [μm] diameter g⁻¹] [Ω] [° C.] Example 9 5.4 0.471.15 0.005 0.005 5.1 0.42 157.1 2.9 220 Example 10 5.4 0.47 1.15 0.0360.036 5.2 0.42 156.9 2.9 224 Example 11 5.4 0.47 1.15 0.005 0.035 5.30.43 151.6 3.3 238 Example 12 5.4 0.47 1.15 0.005 0.035 5.3 0.43 150.83.4 240 Comparative 10.8 0.89 1.15 0.005 0.005 10.1 0.86 154.3 3.8 232Example 4 Comparative 5.4 0.47 1.15 0 0.000 5.1 0.42 156.2 5.2 219Example 5 Comparative 5.4 0.47 1.15 0 0.030 5.2 0.43 151.1 5.4 238Example 6

(Evaluation)

It is found that the positive electrode active materials in Examples 9to 12, which have the respective average particle diameters and therespective particle size distributions according to the presentinvention and to which tungsten was added, have higher capacity andlower positive electrode resistance and are suitable as positiveelectrode active materials for nonaqueous electrolyte secondarybatteries.

On the other hand, it is found that Comparative Example 4, having alarger average particle diameter and a wider particle size distribution,has the same level of battery capacity as Examples 9 to 12, but hashigher positive electrode resistance, and accordingly insufficientoutput characteristics. Also, it is found that Comparative Examples 5and 6, to which tungsten was not added, have considerably higherpositive electrode resistance, and hence have a problem as positiveelectrode active materials for nonaqueous electrolyte secondarybatteries.

What is claimed is:
 1. A transition metal composite hydroxiderepresented by a general formula (1) MxWsAt(OH)2+α (wherein, x+s+t=1,0<s≤0.05, 0<s+t≤0.15, 0≤α≤0.5, M is at least one transition metalselected from Ni, Co and Mn, and A is at least one additive elementselected from B, Al, Sc, Zr, Hf, V, Ta, Cr, and Mo and serving as aprecursor of a positive electrode active material for nonaqueouselectrolyte secondary batteries, wherein the transition metal compositehydroxide is a secondary particle having a spherical shape and composedof aggregation of a plurality of primary particles, the secondaryparticle has an average particle diameter of 3 to 7 μm and an indexindicating a scale of particle-size distribution,[(d90−d10)/average-particle-diameter], of not more than 0.55, and acoating material containing a metal oxide of tungsten and the additiveelement or a metal hydroxide of tungsten and the additive element isformed on surfaces of the secondary particles.
 2. The transition metalcomposite hydroxide according to claim 1, wherein a specific surfacearea is 5 to 30 m2/g.
 3. The transition metal composite hydroxideaccording to claim 1, wherein s+t in the general formula (1) is0.02<s+t≤0.15.
 4. The transition metal composite hydroxide according toclaim 1, wherein the coating material is a mixture containing a tungstenoxide hydrate and aluminum hydroxide.